Renewable Energy in sit

Power Cable Observati

OCS Study

BOEM 2016-008

Pacific Outer Continental Shelf Region

HONDO

Nearshore

11–14 m

Offshore

76–213 m

HARMONY

HERITAGE

(A)

(B)

(C)

(C1

)

Pipe

C A L I F O R N I A

Area

Detailed
ii

This page intentionally left blank.
iii

Renewable Energy in situ Power Cable Observ

Authored by:

Milton S. Love

Mary M. Nishimoto

Scott Clark

Ann S. Bull

Submitted by:

Marine Science Institute

University of California

Santa Barbara, CA 93106

Prepared under:

BOEM Cooperative Agreement No. M11AC00008

The U.S. Department of the Interior

Bureau of Ocean Energy Management

Pacific OCS Region

Camarillo, CA, 93010

 

 April 2016

OCS Study

BOEM 2016-008
iv

Disclaimer

This report was prepared under a cooperative agreement between the Bureau of Ocean Energy Management 

and the University of California, Santa Barbara. The report has been technically reviewed by BOEM and it 

has been approved for publication. The opinions, findings, conclusions, or recommendations in this report 

are those of the authors, and do not necessarily reflect the views and policies of BOEM. Mention of trade 

names or commercial products does not constitute an endorsement or recommendation for use.

Report Availabilit

To download a PDF of this report, go to the U.S. Department of the Interior, Bureau of Ocean Energy 

Management, Environmental Studies Program Information System (ESPIS) website and search on OCS 

Study BOEM 2016-008.

This report can also be downloaded at www.lovelab.id.ucsb.edu.

Citation

Love, M. S., M. M. Nishimoto, S. Clark, and A. S. Bull. 2016. Renewable Energy in situ Power Cable 

Observation. U.S. Department of the Interior, Bureau of Ocean Energy Management, Pacific OCS 

Region, Camarillo, CA. OCS Study 2016-008. 86 pp.
v

Table of Content

Technical Summary vi

Executive Summary xiii

Chapter 1. Introduction to Chapters 2 and 3 1

Chapter 2. Task 1 Inshore Survey 3

Chapter 3. Task 2 Offshore Survey 44

List of Figur

Figure 1-1. 2

Figure 2-1. 13

Figure 2-2. 14

Figure 2-3. 15

Figure 2-4. 16

Figure 2-5. 17

Figure 2-6. 18

Figure 2-7. 19

Figure 2-8. 20

Figure 2-9. 21

Figure 2-10. 22

Figure 2-12. 23

Figure 2-12. 24

Figure 2-13. 25

Figure 2-14. 26

Figure 2-15. 27

Figure 2-16. 28

Figure 2-17. 29

Figure 3-1. 57

Figure 3-2. 58

Figure 3-3. 59

Figure 3-4. 60

Figure 3-5. 61

Figure 3-6. 62

Figure 3-7. 63

Figure 3-8. 64

Figure 3-9. 65

Figure 3-10. 66

Figure 3-11. 67

List of Tabl

Table 2-1. 30

Table 2-2. 31

Table 2-3. 32

Table 2-4. 33

Table 2-5. 34

Table 2-6. 35

Table 2-7. 36

Table 2-8. 37

Table 2-9. 38

Table 2-10. 39

Table 2-11. 40

Table 2-12. 41

Table 2-13. 42

Table 2-14. 43

Table 3-1. 68

Table 3-2. 70

Table 3-3. 71

Table 3-4. 72

Table 3-5. 73

Table 3-6. 74

Table 3-7. 75

Table 3-8. 76

Table 3-9. 77

Table 3-10. 78

Table 3-11. 79

Table 3-12. 80

Table 3-13. 81

Table 3-14. 82

Table 3-15. 83

Table 3-16. 84

Table 3-17. 85
vi

Technical Su

Study Title: Renewable Energy in situ Power Cable Observati

Report Title: Renewable Energy in situ Power Cable Observatio

Contract Number: M11AC0000

Sponsoring OCS Region: Paci

Applicable Planning Area: Southern Californ

Fiscal Years of Project Funding: 2011, 2012, 2

Completion Date of the Report: April 2016

Costs: FY 2011: $849,395; FY 2012: $100,000; FY 2013: $283,265

Cumulative Project Cost: $1,232,660

Principal Investigator: Milton Lov

Affiliation: University of California, Santa Barbara; Marine Science Institut

Address: Santa Barbara, CA 9310

Principal Investigator: Milton Lov

Key Words: EMF, electromagnetic fields, renewable energy, power cable

Background and Objectiv

It is likely that for the foreseeable future, offshore renewable energy technologies (e.g., wind and wave) will 

focus on the generation of electricity. These technologies harness energy from an array of individual devices 

and, through power cables, send electricity to shore via cables. These cables will transmit either alternating 

current or direct current, and, if the cable uses alternating current, this current will generate both electric 

and magnetic fields.

Research has shown that some cartilaginous and bony fishes, as well as at least some invertebrates, are 

sensitive to electromagnetic fields (EMF) and that these fields can alter the behavior of these organisms 

(Kalmin 1982, Formicki et al. 2004, Tanski et al. 2005). However, worldwide, very few studies have been 

conducted to document the effects of EMF on marine organisms in situ (Ohman et al. 2007). Only one 

survey on the Pacific Coast has examined, in the marine environment, the role that EMF emitted from 

a cable might play. That study, Barry et al. (2008), found that longnose skate (Raja rhina) appeared to 

have been attracted to an energized sea-bed cable. However, it should be noted that rather than comparing 

energized and unenergized cables, this survey compared organism densities along a sea bed before and after 

an energized cable was installed. Thus it was difficult to differentiate the effects of the EMF emanating from 

the cable from the effects of the cable structure itself.

Submarine transmission cables that power offshore oil platforms in the Pacific Region provide a unique 

opportunity to assess potential behavior and reaction of electromagnetic-sensitive species to industry 

activities. In particular, the chance occurrence of both energized and unenergized cables in a corridor on the 

seafloor within the Santa Ynez Unit Offshore Southern California Planning Area, allows for an experiment 

testing the effects of EMF on marine organisms. The identical cables stretch several miles from Platforms 

Heritage, Harmony, and Hondo (at depths to about 326 m) to Los Flores on the mainland. The cables run 

from the platforms toward the mainland to a sea floor depth of 10 m and from there are buried inshore. One 

unenergized cable runs from a platform to the border of federal and state waters at a bottom depth of about 

150 m. All of these cables use the industry standards of the power cables that will be used for connecting 

devices (35 KV) within renewable energy installations. These cables were emplaced concurrently by the 

manufacturer. Thus, the cables form a natural experiment, allowing a comparison of an energized power 
vii

cable with one that is unenergized to determine the potential impacts from electromagnetic fields while 

controlling for the habitat effect contributed by the cables themselves.

The goal of this study was to more fully understand the potential effects of energized, seabed deployed, 

power cables on marine organisms.

Specific objectives of this study were to determine:

1) The differences among fish and invertebrate communities associated with energized and unenergized 

cable habitat and those communities in soft seafloor habitats lacking cables.

2) Whether electrosensitive species that are regionally important such as sharks and rays respond (via 

either attraction or repulsion) to the EMF’s of an in situ power transmission cable.

3) The strength, spatial extent, and variability of EMF’s along both energized and unenergized cables.

4) The potential effectiveness of the commonly proposed mitigation of cable burial.

Knowledge gained from this study will be directly applicable to renewable energy projects not only in the 

Pacific OCS region, but to any OCS planning area.

Description

The research was divided into two parts: Task 1 took place in inshore waters (10–14 m) and Task 2 in 

offshore waters (76–213 m). Here following, we will divide the descriptions and significant results of our 

research into those two categories.

Task 1

Between 1 February 2012 and 26 February 2014 using scuba, we surveyed the fishes, invertebrates, and 

marine plants living on two energized submarine power cables, adjacent pipe, and natural habitat. Along 

cable, pipe, and over sandy bottom, we installed six permanent 30 m-long transects; three at a shallow 

depth (10–11 m) and three in slightly deeper waters (13–14 m depth). The end of the shallow transects and 

beginning of the deep ones were separated by about 120 m. The beginning and ending of each transect at 

each site was marked by sand anchors as was each 5 m segment along each transect. Transects were 2 m wide, 

centered on the pipe or cable or an imaginary line between sand anchors that delineated the sandy control 

transect. During the surveys, we measured the electromagnetic fields (EMF) emitted by the cable, pipe, and 

natural habitat. Fishes and plant surveys were conducted from the beginning to end of the study — from 

1 February 2012 to 26 February 2014. Invertebrate surveys were conducted beginning on 22 June 2012 and 

continued until the end of the study. We conducted a total of 38 days of fish surveys, 30 days of invertebrate 

studies, and 38 days of plant studies during the three years.

Task 2

We conducted surveys of energized and unenergized cables and of the nearby sea floor during 2012 (6–9 

October), 2013 (3–5 October) and 2014 (23–25 October) at depths between 76 and 213 m using a manned 

submersible. During 2012, only the east side of each cable was surveyed, while in 2013 and 2014 we surveyed 

both sides of the cables at similar depths. All natural habitat surveys were conducted between 100 and about 

500 m from the nearest cable. 

In 2012, we measured the EMF levels at three distances from energized Cable A. These measurements were 

taken at four locations along the cable (at bottom depths of 108 m, 112 m, 135 m, and 158 m). In 2013 and 

2014, we measured EMF on all energized and unenergized cables on the cable at one location each, and on 

the sea floor.
viii

Significant Result

Task 1

Over the course of the study, average EMF levels at the two cables (A and B) were statistically similar (Cable 

A = 73.0μT, Cable B = 91.4μT) and were much higher at the two cables than at either the pipe (average = 

0.5μT) or sand (0μT)

Fishes 

Overall, our study demonstrated that 1) the fish communities on cables, pipe, and natural habitat 

strongly overlapped (global R=0.097, p=0.01) and 2) the difference between the shallower and deeper fish 

communities was negligible (global R=0.097, p=0.001). 

Over all habitats, we observed 4,671 individuals of a minimum of 44 species. Dominant species included 

adults of benthic-oriented, schooling taxa (i.e., kelp perch, senorita, white seaperch, and shiner perch), 

young-of-the-year (YOY) rockfishes that had newly settled out of the plankton (particularly black-andyellow, gopher, and kelp rockfishes), and relatively solitary substrate-oriented species (i.e., sanddabs and 

kelp perch). Senorita, sanddabs, white seaperch, YOY rockfishes, and kelp perch were the most abundant 

taxa. Cables: At least 35 species and 1,721 individuals were observed over the energized cables. Senorita, 

sanddabs, kelp perch, white seaperch, and YOY rockfishes were most abundant (Table 2-4). Pipe: The 

number of taxa (37) and individuals (1,829) were similar to those observed on the cables. Senorita, YOY 

rockfishes, vermilion rockfish YOY, pile perch, black perch, and sanddabs were the most important taxa on 

the pipe (Table 2-5). Natural Habitat: Fewest species (25) and individuals (1,121) were observed over the 

natural habitat. Shiner perch, sanddabs, senorita, YOY shortbelly rockfish, white seaperch, and tubesnout 

were most often observed here (Table 2-6). 

All of the fish communities were composed primarily of small fishes and the majority of these individuals 

were less than 20 cm long. The mean length of fishes varied significantly among the three habitats (Welch’s 

Test, F = 43.7, df = 2, p <.0001) as did the size distributions. However, we note that the difference of mean 

lengths among sites is very small and it is unlikely that these differences, although statistically significant, 

are biologically meaningful. The abundance of all fishes combined varied seasonally at every site. In general, 

fishes were more abundant from early spring through early fall at all sites. This was reflective of the seasonal 

influx of newly settled rockfishes, young seaperches, and the general increase in fish abundance in nearshore 

waters that takes place as the turbulent winter waters subside.

Invertebrates

Similar to the fish assemblages, the invertebrate communities on the cables, pipe, and natural habitats were 

quite similar overall (global R=0.111, p=0.001) and the shallower and deeper invertebrate assemblages were 

indistinguishable (global R=0.000, p=0.51). 

Over all habitats, we observed a total of 822 individuals comprising a minimum of 19 species. Bat star, 

several species of sea stars, purple urchin (but noted on only one occasion), California sea hare, Comb sea 

star, and Kellet’s whelk were observed most often. By group, sea stars were the most abundant, comprising 

56.8% of all invertebrates recorded. Cables: We observed 157 individuals of at least 15 species at the cable 

sites. Bat star, sea stars, and California sea hare were most abundant. Pipe: Four hundred and forty two 

individual invertebrates, the most of any site, were observed at the pipe. However, 100 of these individuals 

were comprised of a one-time recorded aggregation of purple sea urchin. Like the cables, we recorded 15 

species along the pipe. Natural Habitat: Bat star and Kellet’s whelk predominated in the natural habitat, 

where we recorded 223 individuals, of 13 species. 
ix

Overall, the numbers of invertebrates living at the study sites remained fairly constant over the course of 

the study. What changes occurred were due to influxes of sea stars and bat stars. Of the eight most common 

species observed, the densities of five species ( sea stars, bat star, sea cucumbers, and rock crabs) varied with 

site. Between cables and pipe, densities of four species ( sea stars, bat stars, sea cucumbers, and rock crabs) 

were different. sea stars, bat stars, and sea cucumbers were more abundant at the pipe and rock crabs were 

more often encountered at the cable. The densities of three taxa or taxa groups, sea stars, California sea hare, 

and sea cucumbers were higher at the pipe than at the natural habitat. Lastly, rock crabs and California sea 

hare were found at higher densities at the cables compared to natural habitat and, contrarily, bat stars were 

more abundant at the natural habitat.

Plants

Unlike the fish and invertebrate assemblages, the plant communities of the three sites were different. First, 

there were intra-site differences in the shallower and deeper plant communities within the cables and pipe 

habitats, although not in the natural habitat. In addition, there were differences in the plant communities 

between the three habitats (global R=0.986, p=0.001; R>0.8, p=0.001).

Over all habitats, a total of 72,999 individual plants (many likely observed repeatedly on sequential survey 

days) were tallied, comprising at least five species. Overall, Zostera marina was most abundant, followed by 

Pterygophora californica, Cystoseira spp., Laminaria spp., and Macrocystis pyrifera. Cables: Among all plants, 

Pterygophora californica dominated the cable community, although Cystoseira spp. and Laminaria spp. 

were not uncommon. Pterygophora californica was very abundant on Cable B (particularly shallower), but 

absent from Cable A (although both were energized). Eelgrass grew on the sand near the cable. Macrocystis 

pyrifera grew very sparsely on the shallower Cable B habitat, was more common on the shallower part of 

Cable A, and was essentially absent from the deeper cables. Pipe: Cystoseira spp. and Laminaria spp. were 

by far the most common plants on the pipe. Cystoseira spp. was nearly twice as abundant shallower than 

deeper while Laminaria spp. was almost absent from the shallower site and nearly as abundant as Cystoseira 

spp. deeper. Relatively few P. californica were observed on the pipe and both M. pyrifera and Z. marina were 

almost absent. Natural Habitat: Zostera marina was the only plant growing on the sandy sea floor of the 

natural habitat. It was dense at both the shallower and deeper sites. With the exception of Z. marina living 

on the natural habitat, we did not observe any strong seasonality in plant densities. Densities of Z. marina in 

both the shallower and deeper areas tended to increase over the course of the study.

Regarding the specific objectives of this study: 

1) The differences among fish and invertebrate communities associated with energized and unenergized 

cable habitat and those communities in soft seafloor habitats lacking cables.

We did not find any biologically significant differences among fish and invertebrate communities between 

energized cables, pipe, and natural habitat. In particular, only three species of fish showed statistically 

significant, but slight, differences in densities between the cables and pipe. Plant communities did differ 

among habitats and within habitats between depths. These differences were almost certainly structure and 

depth, rather than EMF, related.

2) Whether electro-sensitive species that are regionally important, such as sharks and rays, respond (via 

either attraction or repulsion) to the EMFs of an in situ power transmission cable.

We observed only one elasmobranch individual, a swell shark, during the course of this study. Thus, it would 

appear that the EMFs generated by these energized cables are either unimportant to these organisms or that 

at least other environmental factors take precedence.
x

3) The strength, spatial extent, and variability of EMFs along both energized and unenergized cables.

The strength of the EMF along the energized cable was relatively stable over time and along its length. The 

EMF produced by the energized cables diminishes to background levels about one meter away from the 

cable. Similarly, both the pipe and natural habitat sites had extremely small or undetectable EMFs.

4) The potential effectiveness of the commonly proposed mitigation of cable burial.

Given the rapidity with which the EMF produced by the energized cables diminishes and the lack of response 

to that EMF by the shallower fish and invertebrates, cable burial would not appear necessary strictly for 

biological reasons. In this and similar cases, cable burial, at sufficient depth, would be an adequate tool to 

prevent EMF emissions from being present at the seafloor.

Task 2

In 2012, at all four locations along the energized cable, EMF levels dropped off precipitously with distance 

from the cable and, at one meter from the cable, approached background levels at three of the four locations. 

In general, field strengths on the energized cables were around 100 μT, while those on the unenergized cables 

were very low and near background (sea floor) levels.

Fishes

We found that fish species communities were structured by depth more so than by habitat type (Global 

R=0.176, p=0.001). There was no statistical difference between the fish assemblages along the energized 

and unenergized cables. The natural habitat community statistically differed from both the energized cable 

and unenergized cable communities. Within species (or in several cases species-groups) that formed at least 

one percent of the fishes observed, we found no differences in densities between energized and unenergized 

cables. We did find differences based on cable side (shortspine combfish densities were higher on the west 

side of cables), depth strata (stripetail rockfish, unidentified poachers, shortspine combfish, greenstriped 

rockfish, lingcod, and unidentified eelpouts), and year (halfbanded rockfish, stripetail rockfish, and lingcod).

Total fish densities were significantly higher around the cables than over the natural habitat. Among the more 

important species, densities of halfbanded, stripetail, and greenstriped rockfishes, shortspine combfish, and 

lingcod were higher at the cables and eelpouts were found at higher densities over natural habitat. There 

were no significant differences in the densities of unidentified sanddabs and unidentified poachers. There 

were very slight, but statistically significant, differences in both mean lengths and size distributions of fishes 

among the three study habitats as fishes at the unenergized cables tended to be slightly larger (mean = 14.8 

cm) than those at both natural habitats (mean = 13.7 cm) and energized cables (mean = 13.0 cm). 

Over all habitats we observed 9,675 individuals of at least 41 species. Dominant species included halfbanded, 

stripetail, and greenstriped rockfishes, and lingcod, and unidentified flatfishes, poachers, and combfishes. 

Energized cables: In the vicinity of the energized cables, we observed at least 33 species of fishes, comprising 

4,455 individuals. Halfbanded rockfish dominated this habitat, comprising 56% of all fishes observed and 

present during 82.3% of the transects. Other important species or species groups included unidentified 

flatfishes and poachers, stripetail and shortspine combfish. Unenergized cables: Similar to the fish assemblage 

found around energized cables, there were at least 35 fish species in proximity to the unenergized cables 

and 3,691 individuals. As with the energized cables, halfbanded rockfish were by far the most abundant 

species, comprising 37.4% of all fish observed. Other important species included stripetail and greenstriped 

rockfishes and unidentified flatfishes, poachers, and combfishes. Natural habitats: Fewest species (at least 23) 

and fishes (1,529) were observed on the natural habitats. Here, unidentified flatfishes, eelpouts, poachers, 

combfishes, sanddabs and halfbanded rockfish predominated. 
xi

Invertebrates

The structure of the invertebrate communities living around energized and unenergized cables and natural 

habitats was similar to that of fishes. We found that invertebrate communities were structured by habitat 

type and depth. Similar to the fishes, there was no statistical difference between the invertebrate assemblages 

along the energized and unenergized cables. The natural habitat community of invertebrates strongly 

differed from the energized cable and unenergized cable communities.

To determine if there were significant differences in species densities between energized and unenergized 

cables, we compared the densities of those important species that comprised at least 1% of individuals 

observed in this study in the same way as for fishes. We did note slight but statistically significant differences 

in densities for only two of nine of the most abundant species. Sand star and black crinoid densities differed 

between unenergized and energized cables [sand star greater at unenergized cables, 4/1/m3

 v 2.7 m3, and 

black crinoid at energized cables, 1.7/m3

 v 0.3/m3]. Three species, thin sea pen, red octopus, and white 

sea urchin differed between cable sides. Seven species, white-plumed anemone, spot prawn, thin sea pen, 

California sea cucumber, red octopus, unidentified Urticina anemone, and black crinoid exhibited bottom 

depth differences. Densities of two species, thin sea pen and sand star, varied among years. 

A number of species were more abundant around the cables than over the natural habitats. Important 

species that were more abundant around cables were white-plumed anemone, spot prawn, thin sea pens, 

California sea cucumber, sand star, and unidentified Urticina anemone. Red octopus and white sea urchin 

were denser over natural habitats and densities of black crinoid did not differ between the two habitats.

Over all habitats, we observed a total of 30,523 invertebrates of at least 43 invertebrate species. The whiteplumed anemone was by far the most abundant animal and comprised 43.4% of all invertebrates recorded. 

Spot prawns, thin sea pens, California sea cucumbers, sand stars, and the red octopuses were also found at 

relatively high densities. Energized cables: We observed 13,388 individuals, of at least 36 species, living on or 

near the energized cables. White-plumed anemones, thin sea pens and spot prawns were the species found in 

highest densities, forming in aggregate 79.7% of all invertebrates observed. California sea cucumbers, sand 

stars, red octopuses, black crinoids, and Urticina anemones were also common. Unenergized cables: At least 

35 species and 14,619 individuals were observed along the unenergized cables. Three species, white-plumed 

anemones, spot prawns, and thin sea pens, were by far the most dense, in aggregate forming 79.2% of all 

invertebrates surveyed. California sea cucumbers, sand stars, red octopus, unidentified Urticina anemones, 

and serpulid worms were also characteristic of this habitat. Natural habitats: We observed the fewest number 

of species (a minimum of 27) and individuals (2,516) over the natural habitat. Thin sea pens, red octopuses, 

white sea urchins and sand stars dominated this habitat, along with smaller numbers of white-plumed 

anemones, fragile pink urchins, California sea cucumbers, and sea slugs.

Regarding the specific objectives of this study: 

1) The differences among fish and invertebrate communities associated with energized and unenergized 

cable habitat and those communities in soft seafloor habitats lacking cables.

We did not observe any significant differences in the fish communities living around energized and 

unenergized cables and natural habitats. A very slight, and likely biologically insignificant, difference in 

mean sizes was observed as fishes at unenergized cables were marginally larger than those around energized 

ones. Overall species diversity and the densities of the most important fish species (define as comprising at 

least 1% of all fishes observed) were higher at the cables than at the natural habitats. This is likely reflective 

of the more complex habitats afforded by the cables than the primarily soft substrata natural habitats. 
xii

Similar to the fish communities, the invertebrate assemblages living around energized and unenergized 

cables and natural habitats were similar to one another and variability between these communities was 

primarily driven by sea floor depth. Among the three habitat types, there were some statistically significant 

differences in densities for all nine of the most abundant species. These differences included: 1) two species, 

sand star and black crinoid, whose densities differed between energized and unenergized cables, 2) three 

species, thin sea pen, red octopus, and white sea urchin which differed between cable sides, 3) seven species, 

white-plumed anemone, spot prawn, thin sea pen, California sea cucumber, red octopus, unidentified 

Urticina anemone, and black crinoid that exhibited bottom depth differences, and 4) two species, thin sea 

pen and sand star, whose densities varied among years. Sand star densities were greater at unenergized 

cables, 4/1/m3

 v 2.7 m3, and black crinoid densities were greater at energized cables, 1.7/m3 v 0.3/m3. 

2) Whether electro-sensitive species that are regionally important, such as sharks and rays, respond 

(via either attraction or repulsion) to the EMFs of an in situ power transmission cable.

We observed very few individuals of electro-sensitive species on the energized or unenergized cables or on 

the natural habitats. Only five ratfish (three at the energized cables and two on the unenergized ones) and 

one California skate (at the unenergized cable) were noted. Thus, we found no compelling evidence that the 

EMF produced by the energized power cables in this study were either attracting or repelling these fishes. 

3) The strength, spatial extent, and variability of EMFs along both energized and unenergized cables.

The EMFs produced by the energized cables were similar both over the three years of the study and along the 

cables. EMF strength dissipated relatively quickly with distance from the cable and approached background 

levels at about one meter from the cable. The EMF at unenergized cables was similar to that found at the 

natural habitats.

4) The potential effectiveness of the commonly proposed mitigation of cable burial.

Given the rapidity with which the EMF produced by the energized cables diminishes and the lack of response 

to that EMF by the fishes and invertebrates in this study, cable burial would not appear necessary strictly for 

biological reasons. In this and similar cases, cable burial, at sufficient depth, would be an adequate tool to 

prevent EMF emissions from being present at the seafloor.

Literature Cite

Barry, J. P., L. Kuhnz, K. Buck, C. Lovera, and P.J. Whaling. 2008. Potential impacts of the MARS cable 

on the seabed and benthic faunal assemblages. Monterey Bay Aquarium Research Institute.

Clarke , K. R. and R. N. Warwic. 2001. Changes in marine communities: an approach to statistical analysis 

and interpretation, 2nd edition. PRIMER-E Ltd, Plymouth.

Formicki, K., M. Sadowski, A. Tanski, A. Korzelecka-Orkisz, and A. Winnicki. 2004. Behavioiur of trout 

(Salmo trutta L.) larvae and fry in a constant magnetic field. J. Appl. Ichthyol. 20:290–294.

Kalminjn, A. J. 1982. Electric and magnetic field detection in elasmobranch fishes. Science 218:916–918.

Ohman, M. C., P. Sigray, and H. Westerberg. 2007. Offshore windmills and the effects of electromagnetic 

fields on fish. Ambio 36:630–633.

Tanski, A., K. Formicki, P. Smietana, M. Sadowski, and A. Winnicki. 2005. Sheltering behaviour of 

spinycheek crayfish (Orconectes limosus) in the presence of an artificial magnetic field. Bull. Fran. 

Peche Pisciculture 376:787–793.
xiii

Renewable Energy in situ Power Cable Observ

Executive Sum

Information Need

In the future, offshore renewable energy is likely to be a major source of power for the United States. Offshore 

renewable energy technologies (e.g., wind and wave) harness energy from an array of individual devices 

and, through power cables, send electricity to shore via cables. These cables will transmit either alternating 

current or direct current, and, if the cable uses alternating current, this current will generate both electric 

and magnetic fields.

Research has shown that some cartilaginous and bony fishes, as well as at least some invertebrates, are 

sensitive to electromagnetic fields (EMF) and that these fields can alter the behavior of these organisms. 

However, worldwide, very few studies have been conducted to document the effects of EMF on marine 

organisms in situ. Only one survey on the Pacific Coast has examined, in the marine environment, the role 

that EMF emitted from a cable might play. That study found that longnose skate (Raja rhina) appeared to 

have been attracted to an energized sea-bed cable. However, it should be noted that rather than comparing 

energized and unenergized cables, this survey compared organism densities along a sea bed before and after 

an energized cable was installed. Thus it was difficult to differentiate the effects of the EMF emanating from 

the cable from the effects of the cable structure itself.

Submarine transmission cables that power offshore oil platforms in the Pacific Region provide a unique 

opportunity to assess potential behavior and reaction of electromagnetic-sensitive species to industry 

activities. In particular, the chance occurrence of both energized and unenergized cables in a corridor on the 

seafloor within the Santa Ynez Unit Offshore Southern California Planning Area, allows for an experiment 

testing the effects of EMF on marine organisms. The identical cables stretch several miles from Platforms 

Heritage, Harmony, and Hondo (at depths to about 326 m) to Los Flores on the mainland. The cables run 

from the platforms toward the mainland to a sea floor depth of 10 m and from there are buried inshore. One 

unenergized cable runs from a platform to the border of federal and state waters at a bottom depth of about 

150 m. All of these cables use the industry standards of the power cables that will be used for

connecting devices (35 KV) within renewable energy installations. These cables were emplaced concurrently 

by the manufacturer. Thus, the cables form a natural experiment, allowing a comparison of an energized 

power cable with one that is unenergized to determine the potential impacts from electromagnetic fields 

while controlling for the habitat effect contributed by the cables themselves.

The goal of this study was to more fully understand the potential effects of energized, seabed deployed, 

power cables on marine organisms.

Specific objectives of this study were to determine:

1) The differences among fish and invertebrate communities associated with energized and unenergized 

cable habitat and those communities in soft seafloor habitats lacking cables.

2) Whether electrosensitive species that are regionally important such as sharks and rays respond (via 

either attraction or repulsion) to the EMF’s of an in situ power transmission cable.
xiv

3) The strength, spatial extent, and variability of EMF’s along both energized and unenergized cables.

4) The potential effectiveness of the commonly proposed mitigation of cable burial.

Knowledge gained from this study will be directly applicable to renewable energy projects not only in the 

Pacific OCS region, but to any OCS planning area.

Research Summar

The research was divided into two parts: Task 1 took place in inshore waters (10–14 m) and Task 2 in 

offshore waters (76–213 m). Here following, we will divide the descriptions and significant results of our 

research into those two categories.

Task 1

Between 1 February 2012 and 26 February 2014 using scuba, we surveyed the fishes, invertebrates, and 

marine plants living on two energized submarine power cables, adjacent pipe, and natural habitat. Along 

cable, pipe, and over sandy bottom, we installed six permanent 30 m-long transects; three at a shallow 

depth (10–11 m) and three in slightly deeper waters (13–14 m depth). The end of the shallow transects and 

beginning of the deep ones were separated by about 120 m. The beginning and ending of each transect at 

each site was marked by sand anchors as was each 5 m segment along each transect. Transects were 2 m wide, 

centered on the pipe or cable or an imaginary line between sand anchors that delineated the sandy control 

transect. During the surveys, we measured the electromagnetic fields (EMF) emitted by the cable, pipe, and 

natural habitat. Fishes and plant surveys were conducted from the beginning to end of the study — from 

1 February 2012 to 26 February 2014. Invertebrate surveys were conducted beginning on 22 June 2012 and 

continued until the end of the study. We conducted a total of 38 days of fish surveys, 30 days of invertebrate 

studies, and 38 days of plant studies during the three years. 

Over the course of the study, average EMF levels at the two cables (A and B) were statistically similar (Cable 

A = 73.0μT, Cable B = 91.4μT) and were much higher at the two cables than at either the pipe (average = 

0.5μT) or sand (0μT).

Fishes 

Overall, our study demonstrated that 1) the fish communities on cables, pipe, and natural habitat 

strongly overlapped (global R=0.097, p=0.01) and 2) the difference between the shallower and deeper fish 

communities was negligible (global R=0.097, p=0.001). 

Over all habitats, we observed 4,671 individuals of a minimum of 44 species. Dominant species included 

adults of benthic-oriented, schooling taxa (i.e., kelp perch, senorita, white seaperch, and shiner perch), 

young-of-the-year (YOY) rockfishes that had newly settled out of the plankton (particularly black-andyellow, gopher, and kelp rockfishes), and relatively solitary substrate-oriented species (i.e., sanddabs and 

kelp perch). Senorita, sanddabs, white seaperch, YOY rockfishes, and kelp perch were the most abundant 

taxa. Cables: At least 35 species and 1,721 individuals were observed over the energized cables. Senorita, 

sanddabs, kelp perch, white seaperch, and YOY rockfishes were most abundant (Table 2-4). Pipe: The 

number of taxa (37) and individuals (1,829) were similar to those observed on the cables. Senorita, YOY 

rockfishes, vermilion rockfish YOY, pile perch, black perch, and sanddabs were the most important taxa on 

the pipe (Table 2-5). Natural Habitat: Fewest species (25) and individuals (1,121) were observed over the 

natural habitat. Shiner perch, sanddabs, senorita, YOY shortbelly rockfish, white seaperch, and tubesnout 

were most often observed here (Table 2-6). 
xv

All of the fish communities were composed primarily of small fishes and the majority of these individuals 

were less than 20 cm long. The mean length of fishes varied significantly among the three habitats (Welch’s 

Test, F = 43.7, df = 2, p <.0001) as did the size distributions. However, we note that the difference of mean 

lengths among sites is very small and it is unlikely that these differences, although statistically significant, 

are biologically meaningful. The abundance of all fishes combined varied seasonally at every site. In general, 

fishes were more abundant from early spring through early fall at all sites. This was reflective of the seasonal 

influx of newly settled rockfishes, young seaperches, and the general increase in fish abundance in nearshore 

waters that takes place as the turbulent winter waters subside.

Invertebrates

Similar to the fish assemblages, the invertebrate communities on the cables, pipe, and natural habitats were 

quite similar overall (global R=0.111, p=0.001) and the shallower and deeper invertebrate assemblages were 

indistinguishable (global R=0.000, p=0.51). 

Over all habitats, we observed a total of 822 individuals comprising a minimum of 19 species. Bat star, 

several species of sea stars, purple urchin (but noted on only one occasion), California sea hare, Comb sea 

star, and Kellet’s whelk were observed most often. By group, sea stars were the most abundant, comprising 

56.8% of all invertebrates recorded. Cables: We observed 157 individuals of at least 15 species at the cable 

sites. Bat star, sea stars, and California sea hare were most abundant. Pipe: Four hundred and forty two 

individual invertebrates, the most of any site, were observed at the pipe. However, 100 of these individuals 

were comprised of a one-time recorded aggregation of purple sea urchin. Like the cables, we recorded 15 

species along the pipe. Natural Habitat: Bat star and Kellet’s whelk predominated in the natural habitat, 

where we recorded 223 individuals, of 13 species. 

Overall, the numbers of invertebrates living at the study sites remained fairly constant over the course of 

the study. What changes occurred were due to influxes of sea stars and bat stars. Of the eight most common 

species observed, the densities of five species ( sea stars, bat star, sea cucumbers, and rock crabs) varied with 

site. Between cables and pipe, densities of four species ( sea stars, bat stars, sea cucumbers, and rock crabs) 

were different. sea stars, bat stars, and sea cucumbers were more abundant at the pipe and rock crabs were 

more often encountered at the cable. The densities of three taxa or taxa groups, sea stars, California sea hare, 

and sea cucumbers were higher at the pipe than at the natural habitat. Lastly, rock crabs and California sea 

hare were found at higher densities at the cables compared to natural habitat and, contrarily, bat stars were 

more abundant at the natural habitat.

Plants

Unlike the fish and invertebrate assemblages, the plant communities of the three sites were different. First, 

there were intra-site differences in the shallower and deeper plant communities within the cables and pipe 

habitats, although not in the natural habitat. In addition, there were differences in the plant communities 

between the three habitats (global R=0.986, p=0.001; R>0.8, p=0.001).

Over all habitats, a total of 72,999 individual plants (many likely observed repeatedly on sequential survey 

days) were tallied, comprising at least five species. Overall, Zostera marina was most abundant, followed by 

Pterygophora californica, Cystoseira spp., Laminaria spp., and Macrocystis pyrifera. Cables: Among all plants, 

Pterygophora californica dominated the cable community, although Cystoseira spp. and Laminaria spp. were 

not uncommon. Pterygophora californica was very abundant on Cable B (particularly shallower), but absent 

from Cable A (although both were energized). Eelgrass grew on the sand near the cable. Macrocystis pyrifera

grew very sparsely on the shallower Cable B habitat, was more common on the shallower part of Cable A, 
xvi

and was essentially absent from the deeper cables. Pipe: Cystoseira spp. and Laminaria spp. were by far the 

most common plants on the pipe. Cystoseira spp. was nearly twice as abundant shallower than deeper while 

Laminaria spp. was almost absent from the shallower site and nearly as abundant as Cystoseira spp. deeper. 

Relatively few P. californica were observed on the pipe and both M. pyrifera and Z. marina were almost 

absent. Natural Habitat: Zostera marina was the only plant growing on the sandy sea floor of the natural 

habitat. It was dense at both the shallower and deeper sites. With the exception of Z. marina living on the 

natural habitat, we did not observe any strong seasonality in plant densities. Densities of Z. marina in both 

the shallower and deeper areas tended to increase over the course of the study.

Task 2

Our surveys of the offshore marine communities were conducted off the coast of Las Flores Canyon, southern 

California (34°27.6 ́N, 120°02.7 ́W). At this site there are four, variously energized and unenergized, 8” 

diameter submarine power cables providing power to three offshore oil platforms. Surveys were conducted 

aboard the research submersibles Dual DeepWorker (2012 and 2014) and DeepWorker (2013). The Dives 

were made in September and October, during daylight hours. 

We conducted belt transects along cables and on the nearby sea floor. These were documented with an 

externally mounted high-definition video camera positioned on the starboard bow of the submersible. All 

transects were 2-m wide and a set of lasers was used to measure transect width. A green and a red laser were 

set at an angle such that they intersected one another at a distance 2 m away from the submersible. The 

submersible followed a path parallel to the cable such that the intersection of the lasers landed on the cable. 

For off-cable (natural sea floor) transects, the crossing lasers were used to delineate the outside edge of each 

transect with the submarine continuing along a straight path along a compass heading for the duration of 

that transect. We identified both fishes and invertebrates to the lowest possible taxon.

In 2012, we measured the EMF levels at three distances from an energized cable. These measurements were 

taken at four locations along the cable (at bottom depths of 108 m, 112 m, 135 m, and 158 m). At all four 

locations, EMF levels dropped off precipitously with distance from the cable and, at one meter from the 

cable, approached background levels at three of the four locations. During 2013 and 2014, we measured 

energized and unenergized cable EMFs at one point on the cable and at nearby natural sea floors. In general, 

field strengths on the energized cables were around 100 μT, while those on the unenergized cables were very 

low and near background (sea floor) levels.

Fishes

We found that fish species communities were structured by depth more so than by habitat type (Global 

R=0.176, p=0.001). There was no statistical difference between the fish assemblages along the energized 

and unenergized cables. The natural habitat community statistically differed from both the energized cable 

and unenergized cable communities. Within species (or in several cases species-groups) that formed at least 

one percent of the fishes observed, we found no differences in densities between energized and unenergized 

cables. We did find differences based on cable side (shortspine combfish densities were higher on the west 

side of cables), depth strata (stripetail rockfish, unidentified poachers, shortspine combfish, greenstriped 

rockfish, lingcod, and unidentified eelpouts), and year (halfbanded rockfish, stripetail rockfish, and lingcod).

Total fish densities were significantly higher around the cables than over the natural habitat. Among the more 

important species, densities of halfbanded, stripetail, and greenstriped rockfishes, shortspine combfish, and 

lingcod were higher at the cables and eelpouts were found at higher densities over natural habitat. There 
xvii

were no significant differences in the densities of unidentified sanddabs and unidentified poachers. There 

were very slight, but statistically significant, differences in both mean lengths and size distributions of fishes 

among the three study habitats as fishes at the unenergized cables tended to be slightly larger (mean = 14.8 

cm) than those at both natural habitats (mean = 13.7 cm) and energized cables (mean = 13.0 cm). 

Over all habitats we observed 9,675 individuals of at least 41 species. Dominant species included halfbanded, 

stripetail, and greenstriped rockfishes, and lingcod, and unidentified flatfishes, poachers, and combfishes. 

Energized cables: In the vicinity of the energized cables, we observed at least 33 species of fishes, comprising 

4,455 individuals. Halfbanded rockfish dominated this habitat, comprising 56% of all fishes observed and 

present during 82.3% of the transects. Other important species or species groups included unidentified 

flatfishes and poachers, stripetail and shortspine combfish. Unenergized cables: Similar to the fish assemblage 

found around energized cables, there were at least 35 fish species in proximity to the unenergized cables 

and 3,691 individuals. As with the energized cables, halfbanded rockfish were by far the most abundant 

species, comprising 37.4% of all fish observed. Other important species included stripetail and greenstriped 

rockfishes and unidentified flatfishes, poachers, and combfishes. Natural habitats: Fewest species (at least 23) 

and fishes (1,529) were observed on the natural habitats. Here, unidentified flatfishes, eelpouts, poachers, 

combfishes, sanddabs and halfbanded rockfish predominated. 

Invertebrates

The structure of the invertebrate communities living around energized and unenergized cables and natural 

habitats was similar to that of fishes. We found that invertebrate communities were structured by habitat 

type and depth. Similar to the fishes, there was no statistical difference between the invertebrate assemblages 

along the energized and unenergized cables. The natural habitat community of invertebrates strongly 

differed from the energized cable and unenergized cable communities.

To determine if there were significant differences in species densities between energized and unenergized 

cables, we compared the densities of those important species that comprised at least 1% of individuals 

observed in this study in the same way as for fishes. We did note slight but statistically significant differences 

in densities for only two of nine of the most abundant species. Sand star and black crinoid densities differed 

between unenergized and energized cables [sand star greater at unenergized cables, 4/1/m3

 v 2.7 m3, and 

black crinoid at energized cables, 1.7/m3

 v 0.3/m3]. Three species, thin sea pen, red octopus, and white 

sea urchin differed between cable sides. Seven species, white-plumed anemone, spot prawn, thin sea pen, 

California sea cucumber, red octopus, unidentified Urticina anemone, and black crinoid exhibited bottom 

depth differences. Densities of two species, thin sea pen and sand star, varied among years. 

A number of species were more abundant around the cables than over the natural habitats. Important 

species that were more abundant around cables were white-plumed anemone, spot prawn, thin sea pens, 

California sea cucumber, sand star, and unidentified Urticina anemone. Red octopus and white sea urchin 

were denser over natural habitats and densities of black crinoid did not differ between the two habitats.

Over all habitats, we observed a total of 30,523 invertebrates of at least 43 invertebrate species. The whiteplumed anemone was by far the most abundant animal and comprised 43.4% of all invertebrates recorded. 

Spot prawns, thin sea pens, California sea cucumbers, sand stars, and the red octopuses were also found at 

relatively high densities. Energized cables: We observed 13,388 individuals, of at least 36 species, living on or 

near the energized cables. White-plumed anemones, thin sea pens and spot prawns were the species found in 

highest densities, forming in aggregate 79.7% of all invertebrates observed. California sea cucumbers, sand 
xviii

stars, red octopuses, black crinoids, and Urticina anemones were also common. Unenergized cables: At least 

35 species and 14,619 individuals were observed along the unenergized cables. Three species, white-plumed 

anemones, spot prawns, and thin sea pens, were by far the most dense, in aggregate forming 79.2% of all 

invertebrates surveyed. California sea cucumbers, sand stars, red octopus, unidentified Urticina anemones, 

and serpulid worms were also characteristic of this habitat. Natural habitats: We observed the fewest number 

of species (a minimum of 27) and individuals (2,516) over the natural habitat. Thin sea pens, red octopuses, 

white sea urchins and sand stars dominated this habitat, along with smaller numbers of white-plumed 

anemones, fragile pink urchins, California sea cucumbers, and sea slugs.

Conclusions

Regarding the specific objectives of these studies: 

Task 1

1) The differences among fish and invertebrate communities associated with energized and unenergized 

cable habitat and those communities in soft seafloor habitats lacking cables.

We did not find any biologically significant differences among fish and invertebrate communities between 

energized cables, pipe, and natural habitat. In particular, only three species of fish showed statistically 

significant, but slight, differences in densities between the cables and pipe. Plant communities did differ 

among habitats and within habitats between depths. These differences were almost certainly structure and 

depth, rather than EMF, related.

2) Whether electro-sensitive species that are regionally important, such as sharks and rays, respond (via 

either attraction or repulsion) to the EMFs of an in situ power transmission cable.

We observed only one elasmobranch individual, a swell shark, during the course of this study. Thus, it would 

appear that the EMFs generated by these energized cables are either unimportant to these organisms or that 

at least other environmental factors take precedence.

3) The strength, spatial extent, and variability of EMFs along both energized and unenergized cables.

The strength of the EMF along the energized cable was relatively stable over time and along its length. The 

EMF produced by the energized cables diminishes to background levels about one meter away from the 

cable. Similarly, both the pipe and natural habitat sites had extremely small or undetectable EMFs.

4) The potential effectiveness of the commonly proposed mitigation of cable burial.

Given the rapidity with which the EMF produced by the energized cables diminishes and the lack of response 

to that EMF by the shallower fish and invertebrates, cable burial would not appear necessary strictly for 

biological reasons. In this and similar cases, cable burial, at sufficient depth, would be an adequate tool to 

prevent EMF emissions from being present at the seafloor.

Task 2

1) The differences among fish and invertebrate communities associated with energized and unenergized 

cable habitat and those communities in soft seafloor habitats lacking cables.

We did not observe any significant differences in the fish communities living around energized and 

unenergized cables and natural habitats. A very slight, and likely biologically insignificant, difference in 

mean sizes was observed as fishes at unenergized cables were marginally larger than those around energized 
xix

ones. Overall species diversity and the densities of the most important fish species (define as comprising at 

least 1% of all fishes observed) were higher at the cables than at the natural habitats. This is likely reflective 

of the more complex habitats afforded by the cables than the primarily soft substrata natural habitats. 

Similar to the fish communities, the invertebrate assemblages living around energized and unenergized 

cables and natural habitats were similar to one another and variability between these communities was 

primarily driven by sea floor depth. Among the three habitat types, there were some statistically significant 

differences in densities for all nine of the most abundant species. These differences included: 1) two species, 

sand star and black crinoid, whose densities differed between energized and unenergized cables, 2) three 

species, thin sea pen, red octopus, and white sea urchin which differed between cable sides, 3) seven species, 

white-plumed anemone, spot prawn, thin sea pen, California sea cucumber, red octopus, unidentified 

Urticina anemone, and black crinoid that exhibited bottom depth differences, and 4) two species, thin sea 

pen and sand star, whose densities varied among years. Sand star densities were greater at unenergized 

cables, 4/1/m3

 v 2.7 m3, and black crinoid densities were greater at energized cables, 1.7/m3 v 0.3/m3. 

2) Whether electro-sensitive species that are regionally important, such as sharks and rays, respond (via 

either attraction or repulsion) to the EMFs of an in situ power transmission cable.

We observed very few individuals of electro-sensitive species on the energized or unenergized cables or on 

the natural habitats. Only five ratfish (three at the energized cables and two on the unenergized ones) and 

one California skate (at the unenergized cable) were noted. Thus, we found no compelling evidence that the 

EMF produced by the energized power cables in this study were either attracting or repelling these fishes. 

3) The strength, spatial extent, and variability of EMFs along both energized and unenergized cables.

The EMFs produced by the energized cables were similar both over the three years of the study and along the 

cables. EMF strength dissipated relatively quickly with distance from the cable and approached background 

levels at about one meter from the cable. The EMF at unenergized cables was similar to that found at the 

natural habitats.

4) The potential effectiveness of the commonly proposed mitigation of cable burial.

Given the rapidity with which the EMF produced by the energized cables diminishes and the lack of response 

to that EMF by the fishes and invertebrates in this study, cable burial would not appear necessary strictly for 

biological reasons. In this and similar cases, cable burial, at sufficient depth, would be an adequate tool to 

prevent EMF emissions from being present at the seafloor.
xx

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1

Chapter 1. Introduction to Chapter

It is likely that for the foreseeable future, offshore renewable energy technologies will focus on the generation 

of electricity from renewable resources (e.g., wind and wave). These technologies harness energy from an 

array of individual devices and, through power cables, send electricity to shore via cables. These cables will 

transmit either alternating current or direct current, and, if the cable uses alternating current, this current 

will generate both electric and magnetic fields around these cables.

Research has shown that cartilaginous and some bony fishes, as well as at least some invertebrates, are 

sensitive to electromagnetic fields (EMF) and that these fields can alter the behavior of these organisms 

(Kalmijn 1982, Formicki et al. 2004, Tanski et al. 2005 and summarized in Normandeu et al. 2011). However, 

worldwide, only a few studies have been conducted to document the effects of EMF on marine organisms 

in situ (DONG Energy and Vattenfall 2006, Ohman et al. 2007, Westerberg and Lagenfelt 2008) or in a 

semi-artificially enclosed mesocosm (Gill et al. 2012). These studies have yielded either equivocal, or at best 

subtle, evidence of marine organism responding to artificially induced EMF in a natural or semi-natural 

environment.

Submarine transmission cables that power offshore oil platforms in the Pacific Region provide a unique 

opportunity to assess potential behavior and reaction of electromagnetic-sensitive species to industry 

activities. In particular, the chance occurrence of both energized and unenergized cables, and a pipeline 

leading to the platforms, in a corridor on the seafloor within the Santa Ynez Unit Offshore Southern 

California Planning Area (Figure 1-1), allows for experiments testing the effects of EMF on marine organisms. 

Identical cables (emplaced concurrently by the manufacturer) stretch several miles from Las Flores on the 

mainland to Platforms Heritage, Harmony, and Hondo (at depths to about 326 m). The cables were laid on 

the surface of the seafloor and intentionally were buried from shore out to a depth of 10 m. One of the cables 

is unenergized, because it has been cut at the border of federal and state waters (about 150 m bottom depth), 

and the entire length of the cable in state waters has been removed. All of these power cables are industry 

standard, the type that will be used for connecting devices (35 KV) within renewable energy installations. 

Thus, the cables and pipe form a natural experiment, allowing a comparison of energized and unenergized 

power cables, and pipe to determine the potential impacts from electromagnetic fields while controlling for 

the habitat effect contributed by the cables themselves. 

The goal of this study was to more fully understand the potential effects of energized and seabed deployed 

power cables on marine organisms.

Specific objectives of this study were to determine:

1) The differences among fish and invertebrate communities associated with energized and unenergized 

cable habitat and those communities in soft seafloor habitats lacking cables.

2) Whether electro-sensitive species that are regionally important, such as sharks and rays, respond (via 

either attraction or repulsion) to the EMFs of an in situ power transmission cable.

3) The strength, spatial extent, and variability of EMFs along both energized and unenergized cables.

4) The potential effectiveness of the commonly proposed mitigation of cable burial.
2

Literature Cite

DONG Energy and Vattenfall A/S. Review report 2005. The Danish offshore wind farm demonstration project: 

Horns Rev and Nysted offshore wind farms environmental impact assessment and monitoring. 

Prepared for The Environmental Group of the Danish Offshore Wind Farm Demonstration Projects.

Formicki, K., M. Sadowski, A. Tanski, A. Korzelecka-Orkisz, and A. Winnicki. 2004. Behaviour of trout 

(Salmo trutta L.) larvae and fry in a constant magnetic field. J. Appl. Ichthyol. 20:290–294.

Gill, A. B., M. Bartlett, and F. Thomsen. 2012. Potential interactions between diadromous fishes of U.K. 

conservation importance and the electromagnetic fields and subsea noise from marine renewable 

energy developments. J. Fish Biol. 81:664–695.

Kalmijn, A. J. 1982. Electric and magnetic field detection in elasmobranch fishes. Science 218:916–918.

Normandeu, Exponent, T. Tricas, and A. Gill. 2011. Effects of EMFs from undersea power cables on 

elasmobranchs and other marine species. U. S. Dep. of the Interior, Bureau of Ocean Energy 

Management, Regulation, and Enforcement, Pacific OCS Region, Camarillo, CA. OCS Study 

BOEMRE 2011-09.

Ohman, M. C., P. Sigray, and H. Westerberg. 2007. Offshore windmills and the effects of electromagnetic 

fields on fish. Ambio 36:630–633.

Tanski, A., K. Formicki, P. Smietana, M. Sadowski, and A. Winnicki. 2005. Sheltering behaviour of spinycheek 

crayfish (Orconectes limosus) in the presence of an artificial magnetic field. Bull. Fran. Peche 

Pisciculture 376:787–793.

Westerberg, H. and I. Lagenfelt. 2008. Sub-sea power cables and the migration behaviour of the European 

eel. Fish. Manage. Ecol. 15:369–375.

Figure Legen

Figure 1-1. Location of the energized and unenergized submarine power cables surveyed. 

HONDO

Nearshore

11–14 m

Offshore

76–213 m

HARMONY

HERITAGE

(A)

(B)

(C)

(C1

)

Pipe

C A L I F O R N I A

Area

Detailed
3

Chapter 2: Inshore 

Abstrac

Between 1 February 2012 and 26 February 2014 using scuba, we surveyed the fishes, invertebrates, and 

marine plants living on two energized submarine power cables, adjacent pipe, and natural habitat. Along 

cable, pipe, and over sandy bottom, we installed six permanent 30 m-long transects; three at a shallow 

depth (10–11 m) and three in slightly deeper waters (13–14 m depth). The end of the shallow transects and 

beginning of the deep ones were separated by about 120 m. The beginning and ending of each transect at 

each site was marked by sand anchors as was each 5 m segment along each transect. Transects were 2 m wide, 

centered on the pipe or cable or an imaginary line between sand anchors that delineated the sandy control 

transect. During the surveys, we measured the electromagnetic fields (EMF) emitted by the cable, pipe, and 

natural habitat. Fishes and plant surveys were conducted from the beginning to end of the study — from 

1 February 2012 to 26 February 2014. Invertebrate surveys were conducted beginning on 22 June 2012 and 

continued until the end of the study. We conducted a total of 38 days of fish surveys, 30 days of invertebrate 

studies, and 38 days of plant studies during the three years. Over the course of the study, average EMF levels 

at the two cables (A and B) were statistically similar (Cable A = 73.0μT, Cable B = 91.4μT) and were much 

higher at the two cables than at either the pipe (average = 0.5μT) or sand (0μT).

Fishes 

Overall, our study demonstrated that 1) the fish communities on cables, pipe, and natural habitat 

strongly overlapped (global R=0.097, p=0.01) and 2) the difference between the shallower and deeper fish 

communities was negligible (global R=0.097, p=0.001). 

Over all habitats, we observed 4,671 individuals of a minimum of 44 species. Dominant species included 

adults of benthic-oriented, schooling taxa (i.e., kelp perch, senorita, white seaperch, and shiner perch), 

young-of-the-year (YOY) rockfishes that had newly settled out of the plankton (particularly black-andyellow, gopher, and kelp rockfishes), and relatively solitary substrate-oriented species (i.e., sanddabs and 

kelp perch). Senorita, sanddabs, white seaperch, YOY rockfishes, and kelp perch were the most abundant 

taxa. Cables: At least 35 species and 1,721 individuals were observed over the energized cables. Senorita, 

sanddabs, kelp perch, white seaperch, and YOY rockfishes were most abundant (Table 2-4). Pipe: The 

number of taxa (37) and individuals (1,829) were similar to those observed on the cables. Senorita, YOY 

rockfishes, vermilion rockfish YOY, pile perch, black perch, and sanddabs were the most important taxa on 

the pipe (Table 2-5). Natural Habitat: Fewest species (25) and individuals (1,121) were observed over the 

natural habitat. Shiner perch, sanddabs, senorita, YOY shortbelly rockfish, white seaperch, and tubesnout 

were most often observed here (Table 2-6). 

All of the fish communities were composed primarily of small fishes and the majority of these individuals 

were less than 20 cm long. The mean length of fishes varied significantly among the three habitats (Welch’s 

Test, F = 43.7, df = 2, p <.0001) as did the size distributions. However, we note that the difference of mean 

lengths among sites is very small and it is unlikely that these differences, although statistically significant, 

are biologically meaningful. The abundance of all fishes combined varied seasonally at every site. In general, 

fishes were more abundant from early spring through early fall at all sites. This was reflective of the seasonal 

influx of newly settled rockfishes, young seaperches, and the general increase in fish abundance in nearshore 

waters that takes place as the turbulent winter waters subside.
4

Invertebrates

Similar to the fish assemblages, the invertebrate communities on the cables, pipe, and natural habitats were 

quite similar overall (global R=0.111, p=0.001) and the shallower and deeper invertebrate assemblages were 

indistinguishable (global R=0.000, p=0.51). 

Over all habitats, we observed a total of 822 individuals comprising a minimum of 19 species. Bat star, 

several species of Pisaster sea stars, purple urchin (but noted on only one occasion), California sea hare, 

Comb sea star, and Kellet’s whelk were observed most often. By group, sea stars were the most abundant, 

comprising 56.8% of all invertebrates recorded. Cables: We observed 157 individuals of at least 15 species at 

the cable sites. Bat star, Pisaster sea stars, and California sea hare were most abundant. Pipe: Four hundred 

and forty two individual invertebrates, the most of any site, were observed at the pipe. However, 100 of these 

individuals were comprised of a one-time recorded aggregation of purple sea urchin. Like the cables, we 

recorded 15 species along the pipe. Natural Habitat: Bat star and Kellet’s whelk predominated in the natural 

habitat, where we recorded 223 individuals, of 13 species. 

Overall, the numbers of invertebrates living at the study sites remained fairly constant over the course 

of the study. What changes occurred were due to influxes of Pisaster sea stars and bat stars. Of the eight 

most common species observed, the densities of five species (Pisaster sea stars, bat star, sea cucumbers, and 

rock crabs) varied with site. Between cables and pipe, densities of four species (Pisaster sea stars, bat stars, 

sea cucumbers, and rock crabs) were different. Pisaster sea stars, bat stars, and sea cucumbers were more 

abundant at the pipe and rock crabs were more often encountered at the cable. The densities of three taxa 

or taxa groups, Pisaster sea stars, California sea hare, and sea cucumbers were higher at the pipe than at 

the natural habitat. Lastly, rock crabs and California sea hare were found at higher densities at the cables 

compared to natural habitat and, contrarily, bat stars were more abundant at the natural habitat.

Plants

Unlike the fish and invertebrate assemblages, the plant communities of the three sites were different. First, 

there were intra-site differences in the shallower and deeper plant communities within the cables and pipe 

habitats, although not in the natural habitat. In addition, there were differences in the plant communities 

between the three habitats (global R=0.986, p=0.001; R>0.8, p=0.001).

Over all habitats, a total of 72,999 individual plants (many likely observed repeatedly on sequential survey 

days) were tallied, comprising at least five species. Overall, Zostera marina was most abundant, followed by 

Pterygophora californica, Cystoseira spp., Laminaria spp., and Macrocystis pyrifera. Cables: Among all plants, 

Pterygophora californica dominated the cable community, although Cystoseira spp. and Laminaria spp. were 

not uncommon. Pterygophora californica was very abundant on Cable B (particularly shallower), but absent 

from Cable A (although both were energized). Eelgrass grew on the sand near the cable. Macrocystis pyrifera 

grew very sparsely on the shallower Cable B habitat, was more common on the shallower part of Cable A, 

and was essentially absent from the deeper cables. Pipe: Cystoseira spp. and Laminaria spp. were by far the 

most common plants on the pipe. Cystoseira spp. was nearly twice as abundant shallower than deeper while 

Laminaria spp. was almost absent from the shallower site and nearly as abundant as Cystoseira spp. deeper. 

Relatively few P. californica were observed on the pipe and both M. pyrifera and Z. marina were almost 

absent. Natural Habitat: Zostera marina was the only plant growing on the sandy sea floor of the natural 

habitat. It was dense at both the shallower and deeper sites. With the exception of Z. marina living on the 

natural habitat, we did not observe any strong seasonality in plant densities. Densities of Z. marina in both 

the shallower and deeper areas tended to increase over the course of the study.
5

Regarding the specific objectives of this study: 

1) The differences among fish and invertebrate communities associated with energized and unenergized 

cable habitat and those communities in soft seafloor habitats lacking cables.

We did not find any biologically significant differences among fish and invertebrate communities between 

energized cables, pipe, and natural habitat. In particular, only three species of fish showed statistically 

significant, but slight, differences in densities between the cables and pipe. Plant communities did differ 

among habitats and within habitats between depths. These differences were almost certainly structure and 

depth, rather than EMF, related.

2) Whether electro-sensitive species that are regionally important, such as sharks and rays, respond (via either 

attraction or repulsion) to the EMFs of an in situ power transmission cable.

We observed only one elasmobranch individual, a swell shark, during the course of this study. Thus, it would 

appear that the EMFs generated by these energized cables are either unimportant to these organisms or that 

at least other environmental factors take precedence.

3) The strength, spatial extent, and variability of EMFs along both energized and unenergized cables.

The strength of the EMF along the energized cable was relatively stable over time and along its length. The 

EMF produced by the energized cables diminishes to background levels about one meter away from the 

cable. Similarly, both the pipe and natural habitat sites had extremely small or undetectable EMFs.

4) The potential effectiveness of the commonly proposed mitigation of cable burial.

Given the rapidity with which the EMF produced by the energized cables diminishes and the lack of response 

to that EMF by the shallower fish and invertebrates, cable burial would not appear necessary strictly for 

biological reasons. In this and similar cases, cable burial, at sufficient depth, would be an adequate tool to 

prevent EMF emissions from being present at the seafloor.

Method

Our scuba surveys of the subtidal marine community were conducted off the coast of Las Flores Canyon, 

southern California (34°27.6 ́N, 120°02.7 ́W) between 1 February 2012 and 26 February 2014 (Figure 2-1). 

At this site there are 1) three 8” diameter submarine power cables (variously energized and unenergized) 

providing power to three offshore oil platforms and 2) a 12” diameter pipe running from the platforms to 

shore (Figure 2-1). The furthest distance between the outermost cable and the pipe is about 40 m.

Prior to beginning the study, we found that sections of cable were exposed and buried by natural disturbances 

and that EMF levels were lower on the sandy substrate directly over the buried cable than on exposed 

cable. Thus to study the effect of the maximum EMF possible, we determined the survey would have to be 

conducted along unburied sections of the cable. Divers observed cables and pipeline for exposed continuous 

30-m long sections, a standard transect length that we and other research groups have used for fish surveys 

in the region. We were able to find appropriate lengths of exposed energized cables (Cables A and B) where 

fixed 30-m long transects could be set at two bottom depths. As Cable C had been cut off and removed from 

state waters, we were unable to find such lengths along this structure. Lastly, unenergized Cable C1 was 

mostly buried and we did not find any exposed 30-m lengths. Thus, for these surveys, we used the nearby 

exposed pipe as a surrogate for the unenergized cable. Overall, then, we surveyed fishes, invertebrates, and 

plants along three habitats: 1) an energized submarine power cable, a pipe, and a sandy, natural, control area 

to the west of both cables and pipe (Figure 2-1). 
6

Along cable, pipe, and over sandy bottom, we installed six permanent 30 m-long transects; three at a shallow 

depth (10–11 m) and three in slightly deeper waters (13–14 m depth). The end of the shallow transects and 

beginning of the deep ones were separated by about 120 m. The beginning and ending of each transect at 

each site was marked by sand anchors as was each 5 m segment along each transect. Transects were 2 m wide, 

centered on the pipe or cable or an imaginary line between sand anchors that delineated the sandy control 

transect. Two divers conducted each survey and surveys were conducted during daylight hours. The first 

diver surveyed fishes. All fishes encountered within 2 m above the substrate were identified to species, and 

counted, and sized (by eye) to the nearest centimeter. The fish survey diver also recorded water temperature 

and horizontal visibility during each transect and, using an EMF detector, recorded the magnitude of 

EMF at the beginning of each survey. Readings were taken with the detector placed directly against the 

cable, pipe, and sand. A second diver followed and recorded the number of plants in the 2 m swath around 

the cable and pipe or on the sand. Plant quantification was used to determine if these structure-forming 

organisms differentially modified the study habitats. The second diver also recorded macroinvertebrates 

(i.e., cnidarians, mollusca, crustaceans, and echinoderms) encountered within the same 2-m-wide sampling 

area. Only individual invertebrates of at least 10 cm in any dimension were recorded.

Statistical analyses included complete surveys comprised of three shallower and three deeper transects along 

the pipe, energized cable, and natural habitat (sand). Only one survey conducted on 22 June 2012 was 

incomplete and excluded. The number of individuals per transect of each species were treated as observations. 

We summarized the data by each shallower and deeper habitat type as time series using untransformed 

densities (observed count per 100 m3

) of fishes. Counts per transect were used for invertebrates and plants, 

because most of the taxa were observed directly on the cable and pipe structures, and density estimates 

based on the 2 m wide x 30 m long transects would be biased.

We used Primer v6 (Clarke and Gorley, 2006) to examine the biological assemblage data in relation to the 

shallower and deeper habitats. The multivariate analyses excluded taxa that occurred in only one survey. The 

observations of fish and invertebrate counts per transect were transformed to log (x+1). Counts of plants 

per transect were square root-transformed. Bray-Curtis similarity coefficients were calculated to quantify 

the resemblance between transect samples, and similarity matrices were generated for fish, invertebrates 

and plants, separately. Natural groupings of samples were examined using hierarchical clustering with the 

group average linkage option and multidimensional scaling (MDS) ordination. To test the null hypothesis 

that there are no assemblage differences between pipe, cable, and natural habitats (factor A), allowing that 

there may be shallower/deeper differences (factor B), we used a two-way crossed analysis of similarity 

(ANOSIM) that operates on the resemblance matrix. The ANOSIM sample test statistic, R, ranges from 0 

(no difference between groups) to 1 (all dissimilarities between the groups are larger than any dissimilarities 

among samples with either group). A statistically significant (p<0.05) but negligibly small R value close 

to 0 indicates that species composition strongly overlap and the difference between groups may not be 

biologically meaningful.

To determine if the abundance of an individual species statistically differed among the three habitat types, 

we ran parametric or nonparametric tests, α=0.05 (JMP, 2015). Analyses were performed on all plant taxa, 

and the most common fishes and invertebrates. Survey dates were excluded when the individual species 

was absent. The observations of counts per transect were transformed to log(x+1). A one-way analysis of 

variance (ANOVA) was performed on shallower and deeper data separately to test for differences among the 

three habitats, and a t-test was used to test for differences between shallower and deeper transects. The Tukey 

Honestly Significant Difference multiple comparison test was used when differences among habitats were 
7

detected. Alternatively when variances were unequal between groups as determined by the Levene test, the 

nonparametric Welch’s ANOVA and Mann-Whitney test were used with the Wilcoxon method for multiple 

comparisons between habitats.

Results

At the beginning of the study we measured the EMF emitted by the power cables in our study site and found 

that two cables, A and B, were energized. We began our cable surveys on energized Cable B. However, on 15 

May 2013, we noted that Cable B had become unenergized and we switched our surveys to energized Cable 

A for the duration of the study. Importantly, we note that both cables A and B had been energized for at least 

several years before Cable B was switched off (D. Gilbert, pers. comm. to M. L.). Fishes and plant surveys 

were conducted from the beginning to end of the study — from 1 February 2012 to 26 February 2014. 

Invertebrate surveys were conducted beginning on 22 June 2012 and continued until the end of the study. 

Surveys were conducted on a total of 38 days (Table 2-1).

Algae, primarily the brown algae Cystoceira spp., Laminaria spp., Pterygophora californica, and Macrocystis 

pyrifera, grew on some of the cables and pipe, and eelgrass, Zostera marina, lived primarily on the natural 

habitat. The algae were attached to the cables and pipe and the eelgrass was rooted in the soft sediment of the 

natural habitat. Cystoceira spp. was present throughout the year on both the shallow and deep transects (it 

was much more abundant on the pipe) (Figure 2-2); Laminaria spp. occurred almost entirely on the deeper 

pipe and cables (Figure 2-3); P. californica was present only on Cable B (more abundantly in shallow waters) 

(Figure 2-4); and M. pyrifera was primarily limited to the shallow areas of Cable A (Figure 2-5). The sandy, 

natural habitat harbored only scattered eelgrass plants early in the study; however this species became more 

abundant in both shallow and deep areas as the survey progressed (Figure 2-6). Although eelgrass did occur 

on the sand next to both cables, it was present in very low numbers.

EMF Levels

Over the course of the study, average EMF levels at the two cables (A and B) were statistically similar (Cable 

A = 73.0μT, Cable B = 91.4μT) and were much higher at the two cables than at either the pipe (average = 

0.5μT) or sand (0μT) (Figure 2-7, Table 2-2).

Fishes

Overall, our study demonstrated that 1) the fish communities on cables, pipe, and natural habitat strongly 

overlapped (global R=0.097, p=0.01; Figure 2-8), and 2) the difference between the shallower and deeper 

fish communities was negligible (global R=0.097, p=0.001; Figure 2-9).

All Habitats: We conducted a total of 38 days of fish surveys during three years. Over all habitats, we observed 

4,671 individuals of a minimum of 44 species (Tables 2-3, 2-4). Dominant species included adults of benthicoriented, schooling taxa (i.e., kelp perch, senorita, white seaperch, and shiner perch), young-of-the-year 

(YOY) rockfishes that had newly settled out of the plankton (particularly black-and-yellow, gopher, and kelp 

rockfishes), and relatively solitary substrate-oriented species (i.e., sanddabs and kelp perch). Senorita, sanddabs, 

white seaperch, YOY rockfishes, and kelp perch were the most abundant taxa. Cables: At least 35 species and 

1,721 individuals were observed over the energized cables. Senorita, sanddabs, kelp perch, white seaperch, and 

YOY rockfishes were most abundant (Table 2-4). Pipe: The number of taxa (37) and individuals (1,829) were 

similar to those observed on the cables. Senorita, YOY rockfishes, vermilion rockfish YOY, pile perch, black 

perch, and sanddabs were the most important taxa on the pipe (Table 2-5). Natural Habitat: Fewest species 

(25) and individuals (1,121) were observed over the natural habitat. Shiner perch, sanddabs, senorita, YOY 

shortbelly rockfish, white seaperch, and tubesnout were most often observed here (Table 2-6). 
8

All of the fish communities were composed primarily of small fishes and the majority of these individuals were 

less than 20 cm long (Figure 2-10). The mean length of fishes varied significantly among the three habitats 

(Welch’s Test, F = 43.7, df = 2, p <.0001) as did the size distributions (Table 2-8). However, we note that the 

difference of mean lengths among sites (Figure 2-10) is very small and it is unlikely that these differences, 

although statistically significant, are biologically meaningful. The abundance of all fishes combined varied 

seasonally at every site (Figure 2-11). In general, fishes were more abundant from early spring through early 

fall at all sites. This was reflective of the seasonal influx of newly settled rockfishes, young seaperches, and 

the general increase in fish abundance in nearshore waters that takes place as the turbulent winter waters 

subside. We note that an unusual increase in fish abundance occurred at the 10–11 m shallow cable and 

pipe stations during the winter of 2014. This may reflect an unusually mild winter, with few storms and thus 

little turbulence, allowing schools of kelp perch, senorita, and white seaperch to occupy shallower than usual 

waters (M. Love, pers. obs.).

While the overall composition of the fish communities of the various habitats was similar, at the species level 

we did observe some differences in abundances (Table 2-9). Although all of the 15 most abundant species 

were found at all sites, nine (i.e., senorita, sanddabs, rockfish YOY, kelp perch, black perch, rainbow perch, 

bocaccio, giant kelpfish, and copper rockfish) varied in abundances between sites. Most of these differences 

were between the cable or pipe and the natural habitat. The abundances of only three taxa or groups of taxa 

(black perch, rockfish YOY, and sanddabs) differed statistically between the cables and pipe. Black perch and 

rockfish YOY were found at higher densities over the pipe and sanddabs were more common along the cable.

Invertebrates

Not unlike the fish assemblages, the invertebrate communities in the cables, pipe, and natural habitats were 

quite similar overall (global R=0.111, p=0.001; Figure 2-12), and the shallower and deeper invertebrate 

assemblages were indistinguishable (global R=0.000, p=0.51; Figure 2-13).

All Habitats: We conducted a total of 30 days of invertebrate studies during three years. A total of 822 

individuals were observed, comprising a minimum of 19 species (Table 2-10). Bat star, several species of 

Pisaster sea stars, purple urchin (but noted on only one occasion), California sea hare, Comb sea star, and 

Kellet’s whelk were observed most often. By group, sea stars were the most abundant, comprising 56.8% of 

all invertebrates recorded. Cables: We observed 157 individuals of at least 15 species at the cable sites. Bat star, 

Pisaster sea stars, and California sea hare were most abundant (Table 2-11). Pipe: Four hundred and forty two 

individual invertebrates, the most of any site, were observed at the pipe. However, 100 of these individuals 

were comprised of a one-time recorded aggregation of purple sea urchin. Like the cables, we recorded 15 

species along the pipe (Table 2-11). Natural Habitat: Bat star and Kellet’s whelk predominated in the natural 

habitat, where we recorded 223 individuals, of 13 species (Table 2-11). 

Overall, the numbers of invertebrates living at the study sites remained fairly constant over the course of the 

study (Figure 2-14). What changes occurred, for instance during fall 2012 at all deeper sites and summerwinter 2013-14 at the deeper pipe site, were due to influxes of Pisaster sea stars and bat stars (Figure 2-15). 

Of the eight most common species observed, the densities of five species (Pisaster sea stars, bat star, sea 

cucumbers, and rock crabs) varied with site (Table 2-12). Between cables and pipe, densities of four species 

(Pisaster sea stars, bat stars, sea cucumbers, and rock crabs) were different. Pisaster sea stars, bat stars, and sea 

cucumbers were more abundant at the pipe and rock crabs were more often encountered at the cable. The 

densities of three taxa or taxa groups, Pisaster sea stars, California sea hare, and sea cucumbers were higher at 

the pipe than at the natural habitat. Lastly, rock crabs and California sea hare were found at higher densities 

at the cables compared to natural habitat and, contrarily, bat stars were more abundant at the natural habitat.
9

Plants

Unlike the fish and invertebrate assemblages, the plant communities of the three sites were different. First, 

there were intra-site differences in the shallower and deeper plant communities (global R=0.626, p=0.001) 

within the cables and pipe habitats, although not in the natural habitat (Figure 2-16). In addition, there were 

differences in the plant communities between the three habitats (global R=0.986, p=0.001; R>0.8, p=0.001, 

for all pairwise comparisons; Figure 2-17).

All Habitats: We conducted a total of 38 days of plant studies during three years. A total of 72,999 individual 

plants (many likely observed repeatedly on sequential survey days) were tallied, comprising at least five 

species (Table 2-13). Overall, Zostera marina was most abundant, followed by Pterygophora californica, 

Cystoseira spp., Laminaria spp., and Macrocystis pyrifera. Cables: Among all plants, P. californica dominated 

the cable community, although Cystoseira spp. and Laminaria spp. were not uncommon (Table 2-14). Note 

that P. californica was very abundant on Cable B (particularly shallower), but absent from Cable A (Figure 

2-4). Eelgrass grew on the sand near the cable. Macrocystis pyrifera grew very sparsely on the shallower Cable 

B habitat, was more common on the shallower part of Cable A, and was essentially absent from the deeper 

cables (Figure 2-5). Pipe: Cystoseira spp. and Laminaria spp. were by far the most common plants on the 

pipe (Table 2-14). Cystoseira spp. was nearly twice as abundant shallower than deeper while Laminaria spp. 

was almost absent from the shallower site and nearly as abundant as Cystoseira spp. deeper (Figures 2-2, 

2-3). Relatively few P. californica were observed on the pipe and both M. pyrifera and Z. marina were almost 

absent. Natural Habitat: Zostera marina was the only plant growing on the sandy sea floor of the natural 

habitat (Table 2-14). It was dense at both the shallower and deeper sites (Figure 2-6). With the exception 

of Z. marina living on the natural habitat, we did not observe any strong seasonality in plant densities. 

Densities of Z. marina in both the shallower and deeper areas tended to increase over the course of the study.

Discussion

We began this study with the understanding that if a species is attracted to an EMF we would expect to find 

that species in disproportionately larger numbers or densities around the energized cables compared to the 

pipe or natural habitat. Similarly, if a taxa is repelled by that EMF we would expect that species to be present 

less often or in lower densities at the cables. However, the presence or absence of an EMF is not the only 

habitat parameter influencing how an organism chooses its habitat and we acknowledge that in this study 

to an extent the cables and pipe differed not only in the production of an EMF but also in the morphology 

of these habitats.

In particular, the pipe was a slightly more complex structure. First, the pipe’s diameter (12”) was somewhat 

greater than that of the two cables (8”). And while the cable was sometimes partially buried, the pipe was 

not. Thus for both reasons the pipe tended to present a somewhat higher profile. In addition, perhaps the 

greatest structural difference between the cables and pipe was the very high density, particularly on the 

shallower pipe, of Cystoceira sp., a brown algae that was essentially absent from the shallower cable. This alga 

forms a dense cover near the bottom and small fishes, particularly YOY rockfishes, will preferentially inhabit 

this complex substratum. Algae also grew on the cable, particularly Macrocystis pyrifera on the shallower 

area of Cable A, and Laminaria sp. on the deeper portion of both cables. However, M. pyrifera does not form 

luxuriant bottom structures and the Laminaria stands, while present, did not present as dense a cover as 

the Cystoceira on the pipe. The sandy natural habitat was the least complex of all three; it’s two-dimensional 

aspect was only broken up by stands of Z. marina. At the start of the study Z. marina was only sporadically 

found and became more abundant over time.
10

Structural variability aside, the results of our study demonstrated that the fish and invertebrate assemblages 

of the three habitats were very similar. Although a few species statistically varied in abundance between the 

cables and pipe, in no instance was a fish or invertebrate species extremely abundant at one of these two 

habitats and extremely rare or absent from the other. And although fishes were statistically larger at the pipe 

than at the cable or natural habitat, we argue that this difference (of less than one-half centimeter between 

pipe and cable and two centimeters between pipe and natural habitat) is not biologically meaningful. 

In particular, we saw no evidence that any species of fish or invertebrate was either preferentially attracted 

to, or repelled by, the EMF emitted by the cables. Any differences in the fish or invertebrate densities between 

cables, pipe, and natural habitat taxa are most likely due to the differences in the physical characteristics of 

these habitats. For instance, the higher densities of YOY rockfishes and black perch at the pipe are most likely 

due to greater densities of understory algae, specifically Cystoseira spp. By the same token, the lower-relief 

cables, which were closer to the sandy sea floor, were a better habitat for soft-bottom dwelling sanddabs. 

Contrary to the fish and invertebrate assemblages, the plant communities on cables, pipe, and natural habitat 

were clearly different from one another. However, if cable EMF were responsible for these differences, we 

would expect to see similarities in plant communities between energized cables A and B and this was not the 

case (Figure 2-16). Rather, it appears that plant communities were driven by site depth (particular among 

the algae) and habitat type (i.e., eelgrass).

We note that this study was not designed to directly determine the behavior of fishes and invertebrates when 

these organisms encounter an energized cable during, for instance, migrations. Rather, we observed the 

integration over time, that is the results, of myriads of such behaviors by many organisms. Understanding 

how individuals within a taxon relate to energized cables would have to involve either tracking (Westerberg 

and Lagenfelt 2008) or caging experiments (Love et al. 2015) or hybrids of the two (Gill et al. 2009). 

In southern California, most along-shore migrations (as distinct from less synchronized movements) are 

conducted by such pelagic species as blue sharks (Prionace glauca) and Pacific sardines (Sardinops sagax). 

The more substrate-associated shallower species (exemplified by the taxa that dominated our survey) tend 

to be either resident (i.e., swell sharks, black perch), make seasonal shallower-deeper movements (rainbow 

perch), or locally disperse as they mature (YOY rockfishes, shiner perch). Given that the EMF emitted from 

the study cables is undetectable beginning at a distance of about one meter (Love et al. 2015, Love unpubl. 

data) it would be unlikely that pelagic and midwater species are affected by this field. In fact, the limited 

range of the EMF implies that only the movements of those species that live close to the bottom would be 

potentially impacted. 

In our study area, some of the bottom-dwelling or bottom-oriented species most likely to respond to 

energized cables are the elasmobranchs: the sharks, skates, and rays. It is probable that all of these fishes 

can detect an EMF and this ability appears to be used for a number of behaviors including migration and 

food detection (Kalmijn 1971, Tricas 1982, Klimley et al. 2005). Moreover, while the actual sensitivity to an 

EMF is known for only a few elasmobranch species, we note that at least two Atlantic species, Carcharhinus 

plumbeus and Sphyrna lewini, are able to detect an EMF in the 25–100 μT range (Meyer et al. 2005); this is 

within the range generated by the current studies’ energized cables.

The shallower habitats of southern California, and specifically this study site, harbor a rich diversity of 

elasmobranchs (Love 2011). These include both motile taxa (e.g., leopard sharks, Triakis semifasciata and 

smoothhounds, Mustelus spp.) and more sedentary species (shovelnose guitarfish, Rhinobatos productus, 
11

thornback, Platyrhinoidis triseriata, and Pacific angel shark, Squatina californica). Given this diversity, it is 

interesting to note that over the course of this study we observed only one elasmobranch individual, a swell 

shark near the pipe. It might be argued that the chances of seeing individuals of the more motile species 

would be small on any given day; although these chances would likely be increased if the animals were 

attracted to the cables. However, if the more sedentary species were similarly attracted, one might expect 

to have encountered them. And again, the absence of these animals from the cable is likely not because the 

EMF generated is below their sensory threshold. Rather, the data strongly imply that of the electro-sensitive 

species in the study area, at least the elasmobranchs are not attracted to the energized cables. Moreover, 

if these organisms were repelled by the EMF one might expect them to be more abundant at the pipe or 

natural habitat, and that was also not the case. 

Our findings are particularly important because, worldwide, the small number of field or semi-field studies 

that have been conducted on how fishes respond to energized power cables have found either little or no 

response (Westerberg and Lagenfelt 2008, DONG Energy and Vattenfall A/S 2006, Love et al. 2015, present 

study) or, arguably, an equivocal one (Gill et al. 2009). One possible explanation is that marine organisms 

respond to human-made EMF differently from those produced in nature. Recent studies demonstrate 

that human-made EMF is inherently different from naturally produced EMF. Naturally produced EMF 

is polarized and consequently more biologically active (Panagopoulos et al. 2015). Thus, it is possible that 

electro-sensitive organisms are able to differentiate between the two types and therefore respond differently 

to each of these stimuli. 

Regarding the specific objectives of this study: 

1) The differences among fish and invertebrate communities associated with energized and unenergized 

cable habitat and those communities in soft seafloor habitats lacking cables.

We did not find any biologically significant differences among fish and invertebrate communities between 

energized cables, pipe, and natural habitat. In particular, only three species of fish showed statistically 

significant, but slight, differences in densities between the cables and pipe. Plant communities did differ 

among habitats and within habitats between depths. These differences were almost certainly structure and 

depth, rather than EMF, related.

2) Whether electro-sensitive species that are regionally important, such as sharks and rays, respond (via 

either attraction or repulsion) to the EMFs of an in situ power transmission cable.

We observed only one elasmobranch individual, a swell shark, during the course of this study. Thus, it would 

appear that the EMFs generated by these energized cables are either unimportant to these organisms or that 

at least other environmental factors take precedence.

3) The strength, spatial extent, and variability of EMFs along both energized and unenergized cables.

The strength of the EMF along the energized cable was relatively stable over time and along its length. The 

EMF produced by the energized cables diminishes to background levels about one meter away from the 

cable. Similarly, both the pipe and natural habitat sites had extremely small or undetectable EMFs.

4) The potential effectiveness of the commonly proposed mitigation of cable burial.

Given the rapidity with which the EMF produced by the energized cables diminishes and the lack of response 

to that EMF by the shallower fish and invertebrates, cable burial would not appear necessary strictly for 

biological reasons. In this and similar cases, cable burial, at sufficient depth, would be an adequate tool to 

prevent EMF emissions from being present at the seafloor.
12

Acknowledgment

We thank Merit McCrea, Donald Macaskill, Jorge Gross, Frank Hurd, Jacob Eurich, Donna Schroeder, 

and Christopher Teague for their field assistance.

Literature Cite

Clarke, K. R. and R. N. Gorley. 2006. PRIMER v6: User Manual/Tutorial. PRIMER-E, Plymouth, 192pp.

DONG Energy and Vattenfall A/S. 2006. Review Report 2005. The Danish Offshore Wind Farm 

Demonstration Project: Horn Rev and Nysted Offshore Wind Farms. Environmental impact 

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offshore-Wind-Power/Environmental-Impacts/Sider/Forside.aspx.

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COWRIE 2.0 Electromagnetic Fields (EMF) Phase 2: EMF-sensitive fish response to EM emissions 

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Ltd. Cowrie-EMF-1-06. 

JMP®, Version 12.0.1. SAS Institute Inc., Cary, NC, 2015.

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Klimley, A. P., R. L. Kihslinger, and J. T. Kelly. 2005. Directional and non-directional movements of bat 

rays, Myliobatis californica, in Tomales Bay, California. Environmental Biology of Fishes 74:79–88.

Lohmann, K. J., N. D. Pentcheff, G. A. Nevitt, G. D. Stetten, R. K. Zimmerfaust, H. E. Jarrard, and L. C. 

Boles. 1995. Magnetic orientation of spiny lobsters in the ocean – experiments with undersea coil 

systems. Journal of Experimental Biology 198:2041–2048.

Love, M. S. 2011. Certainly More Than You Want to Know About the Fishes of the Pacific Coast. Really Big 

Press, Santa Barbara, CA.

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crabs (general Metacarcinus and Cancer) to energized and unenergized undersea power cables in 

southern California, USA. Bulletin of the Southern California Academy of Science 114:33–41.

Meyer, C. G., K. N. Holland, and Y. P. Papastamatiou. 2005. Sharks can detect changes in the geomagnetic 

field. Journal of the Royal Society Interface 2:129–130.

Panagopoulos, D. J., O. Johansson, and G. L. Carlo. 2015. Polarization: a key difference between man-made 

and natural electromagnetic fields, in regard to biological activity. Scientific Reports 5:14914, 1–10, 

DOI: 10.1038/srep14914. 

Tricas, T. 1982. Bioelectric-mediated predation by swell sharks, Cephaloscyllium ventriosum. Copeia 

(4):948–952.

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eel. Fisheries Management and Ecology 15:369–375.
13

Figure 2-1. Schematic illustration of cables, pipe, and natural habitat surveyed by scuba, 1 February 2012–26 February 

2014. Cables A and B were energized and were used in this study. Cable C1 was unenergized and was not used in this 

study as it was mostly buried in the sea floor. Distance between cables, pipe, and natural habitat not drawn to scale.

Depth = 10 m – 11 m

Depth = 13 m – 14 m

120 m

12"

Pipe

Natural

Habitat

8"

Power Cables

Energized Cable Survey Locations

A B C1

12 m 12 m 3 m 3 m
14

Figure 2-2. Number of Cystoseira spp. observed, by survey date, on cables, pipe, and natural habitat surveyed from 

1 February 2012–26 February 2014.

0

50

100

150

200

0

50

100

150

200

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Date

Date

= Pipe

= Sand

Number Number

Number of All Cystoseira spp. by Date

10–11 m transects

13–14 m transects = Cable A

= Cable B

= Pipe

= Sand

= Cable A

= Cable B
15

Figure 2-3. Number of Laminaria spp. observed, by survey date, on cables, pipe, and natural habitat surveyed from 

1 February 2012–26 February 2014.

0

20

40

60

80

100

0

20

40

60

80

100

0

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Date

Date

= Pipe

= Sand

Number Number

Number of All Laminaria spp. by Date

10–11 m transects

13–14 m transects = Cable A

= Cable B

= Pipe

= Sand

= Cable A

= Cable B
16

Figure 2-4. Number of Pterygophora californica spp. observed, by survey date, on tcables, pipe, and natural habitat 

surveyed from 1 February 2012–26 February 2014.

0

200

400

600

800

1000

1200

0

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Date

Date

= Pipe

= Sand

Number Number

Number of All Pterygophora californica by Date

10–11 m transects

13–14 m transects = Cable A

= Cable B

= Pipe

= Sand

= Cable A

= Cable B

200

400

600

800

1050

1200
17

Figure 2-5. Number of Macrocystis pyrifera observed, by survey date, on cables, pipe, and natural habitat surveyed from 

1 February 2012–26 February 2014.

0

5

10

15

20

0

5

10

15

20

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Date

Date

= Pipe

= Sand

Number Number

Number of All Macrocystis pyrifera by Date

10–11 m transects

13–14 m transects = Cable A

= Cable B

= Pipe

= Sand

= Cable A

= Cable B
18

Figure 2-6. Number of Zostera marina observed, by survey date, on cables, pipe, and natural habitat surveyed from 

1 February 2012–26 February 2014.

0

250

500

750

1000

1250

1500

0

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Date

Date

= Pipe

= Sand

Number Number

Number of All Zostera marina by Date

10–11 m transects

13–14 m transects = Cable A

= Cable B

= Pipe

= Sand

= Cable A

= Cable B

250

500

750

1000

1250

1500
19

Figure 2-7. Electromagnetic field levels measured on cables, pipe, and natural habitat surveyed from 1 February 2012–

26 February 2014. Vertical bars represent standard errors.

Habitat

Cable A Cable B Pipe Sand

EMF levels (μT)

0

50

100

150
20

Figure 2-8. A 2-d multiple dimensional scaling model comparing the shallower and deeper fish assemblages on cables, 

pipe, and natural habitat surveyed from 1 February 2012–26 February 2014.

2D Stress: 0.17

All Fishes by Habitat Type

= Pipe

= Sand

= Cable A

= Cable B

x
21

Figure 2-9. A 2-d multiple dimensional scaling model comparing the fish assemblages on cables, pipe, and natural 

habitat (shallower and deeper transects combined) surveyed from 1 February 2012–26 February 2014. 

= Offshore

= Inshore

2D Stress: 0.17

All Fishes Inshore and Offshore
22

Figure 2-10. Length frequencies of all fishes observed on cables, pipe, and natural habitat surveyed from 1 February 

2012–26 February 2014. Count Count Count

100

200

300

0 10 20 30 40 50 60 70 80 90 100

100

200

300

400

0 10 20 30 40 50 60 70 80 90 100

100

200

300

400

0 10 20 30 40 50 60 70 80 90 100

Cables

Length Frequencies of All Fishes Observed

Pipe

Natural

Habitat

x

– = 11.8 cm

x

– = 11.4 cm

x

– = 9.7 cm

Total Length (cm)

Total Length (cm)

Total Length (cm)
23

Figure 2-11. Densities of all fishes observed, by survey date, on cables, pipe, and natural habitat, 1 February 2012–26 

February 2014. 

0

50

100

150

200

0

50

100

150

200

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Date

Date

= Pipe

= Sand

Fish Density 10m3 Fish Density 10m3

Density of All Fishes Observed by Date

10–11 m transects

13–14 m transects = Cable A

= Cable B

= Pipe

= Sand

= Cable A

= Cable B
24

Figure 2-12. A 2-d multiple dimensional scaling model comparing the shallower and deeper invertebrate assemblages 

on cables, pipe, and natural habitat surveyed from 22 June 2012–26 February 2014.

2D Stress: 0.13

Invertebrate Assemblage by Habitat Type

= Pipe

= Sand

= Cable A

= Cable B

x
25

Figure 2-13. A 2-d multiple dimensional scaling model comparing the invertebrate assemblages on cables, pipe, and 

natural habitat (shallower and deeper transects combined) surveyed from 22 June 2012–26 February 2014. 

= Offshore

= Inshore

2D Stress: 0.13

Invertebrate Assemblage Inshore and Offshore
26

Figure 2-14. Densities of all invertebrates observed, by survey date, on cables, pipe, and natural habitat, 22 June 2012–

26 February 2014. 

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Date

Date

= Pipe

= Sand

Number observed

Count of All Invertebrates by Date

10–11 m transects

13–14 m transects = Cable A

= Cable B

= Pipe

= Sand

= Cable A

= Cable B

0

5

10

15

20

25

30

35

Number observed

0

5

10

15

20

25

30

35
27

Figure 2-15. Densities of all sea stars observed, by survey date, on cables, pipe, and natural habitat, 22 June 2012–26 

February 2014. 

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Jan 1, 2012

Apr 1, 2012

Jul 1, 2012

Oct 1, 2012

Jan 1, 2013

Apr 1, 2013

Jul 1, 2013

Oct 1, 2013

Jan 1, 2014

Apr 1, 2014

Date

Date

= Pipe

= Sand

Number observed

Count of All Sea Stars by Date

10–11 m transects

13–14 m transects = Cable A

= Cable B

= Pipe

= Sand

= Cable A

= Cable B

0

5

10

15

Number observed

0

5

10

15
28

Figure 2-16. A 2-d multiple dimensional scaling model comparing the shallower and deeper plant assemblages on 

cables, pipe, and natural habitat surveyed from 1 February 2012–26 February 2014.

= Offshore

= Inshore

2D Stress: 0.08

All Plants Inshore and Offshore
29

Figure 2-17. A 2-d multiple dimensional scaling model comparing the plant assemblages on cables, pipe, and natural 

habitat (shallower and deeper transects combined) surveyed from 1 February 2012–26 February 2014. 

2D Stress: 0.08

All Plants by Habitat Type

= Pipe

= Sand

= Cable A

= Cable B

x
30

2012

1 Feb 22 Feb 8 Mar 27 Mar 12 Apr 24 Apr 9 May 8 Jun 22 Jun

13 Jul 25 Jul 10 Aug 22 Aug 11 Sep 14 Oct 2 Nov 7 Dec

2013

8 Jan 5 Feb 28 Feb 12 Mar 3 Apr 24 Apr 3 May 15 May 14 Jun

9 Jul 16 Aug 30 Aug 13 Sep 30 Sep 18 Oct 8 Nov 20 Nov 6 Dec 31 Dec

2014

15 Jan 12 Feb 26 Feb

Table 2-1. All dates of surveys on energized cables, pipe, and soft sea floor. Fishes and plants were surveyed on all dates; 

invertebrates were surveyed from 22 June 2012 to 26 February 2014. Surveys were conducted on energized Cable B 

from 1 February 2012 to 3 May 2013 and on energized Cable A from 15 May 2013 to 26 February 2014.
31

Site Site Mean

Difference Standard Error Z p-value

Cable B Cable A 5.95 4.15 1.43 0.15

NH Cable A -32.46 4.40 -7.38 <.0001

Pipe Cable A -34.46 5.30 -6.50 <.0001

Pipe Cable B -36.39 5.30 -6.87 <.0001

NH Cable B -36.97 4.67 -7.92 <.0001

NH Pipe -43.74 5.34 -8.18 <.0001

Table 2-2. Wilcoxon test values comparing EMF field strengths of two energized cables, pipe, and natural habitat, 

2012–2014. NH = natural habitat.
32

Barred sand bass Paralabrax nebulifer

Bat ray Myliobatis californica

Black perch Embiotoca jacksoni

Blackeye goby Rhinogobius nicholsii

Blue rockfish Sebastes mystinus

Bocaccio1 Sebastes paucispinis

Brown rockfish Sebastes auriculatus

Cabezon Scorpaenichthys marmoratu

Calico rockfish Sebastes dalli

California halibut Paralichthys californicus

California lizardfish Synodus lucioceps

C-O Sole Pleuronichthys coenosus

Copper rockfish Sebastes caurinus

Curlfin sole Pleuronichthys decurrens

Giant kelpfish Heterostichus rostratus

Gopher rockfish Sebastes carnatus

Grass rockfish Sebastes rastrelliger

Halfbanded rockfish Sebastes semicinctus

Horn shark Heterodontus francisci

Kelp bass Paralabrax clathratus

Kelp greenling Hexagrammos decagrammus

Kelp perch Brachyistius frenatus

Kelp rockfish Sebastes atrovirens

Lavender sculpin Leiocottus hirundo

Lingcod Ophiodon elongatus

Olive/yellowtail rockfish2 Sebastes serranoides/S. flavidus

Painted greenling Oxylebius pictus

Pile perch Damalichthys vacca

Rainbow seaperch Hypsurus caryi

Rock wrasse Halichoeres semicinctus

Round stingray Urobatis halleri

Sarcastic fringehead Neoclinus blanchardi

Senorita Oxyjulis californica

Sharpnose seaperch Phanerodon atripes

Shiner perch Cymatogaster aggregata

Shortbelly rockfish3 Sebastes jordani

Striped kelpfish Gibbonsia metzi

Swell shark Cephaloscyllium ventriosum

Tubesnout Aulorhynchus flavidus

Unidentified kelpfish Gibbonsia spp.

Unidentified midshipman Porichthys sp.

Unidentified perch Family Embiotocidae

Unidentified pipefish Syngnathus spp.

Unidentified rockfish YOY4 Sebastes spp.

Unidentified ronquil Rathbunella sp.

Unidentified sanddab5 Citharichthys spp.

Unidentified sculpin Family Cottidae

Vermilion rockfish6 Sebastes miniatus

White seaperch Phanerodon furcatus

1

Young-of-the-year.

2

Young-of-the-year.

3

Young-of-the-year.

4

These were young-of-the-year rockfishes of the following species: Sebastes atrovirens, Sebastes carnatus, 

or Sebastes chrysomelas (black-and-yellow rockfish). 5

Probably primarily speckled sanddab, Citharichthys stigmaeus.

6

Young-of-the-year.

Table 2-3. Common and scientific names of fishes observed by scuba at bottom depths of 10–11 m and 13–14 m over 

energized cables, pipe, and natural habitat in southern California, 2012–2014.
33

Species Number Abundance FO

Senorita 976 20.9 26

Unidentified sanddabs1 647 13.9 38

White seaperch 352 7.5 24

Shiner perch 334 7.2 8

Unidentified rockfish YOY2 331 7.1 23

Kelp perch 278 6.0 25

Vermilion rockfish 255 5.5 17

Shortbelly rockfish 190 4.1 1

Black perch 187 4.0 23

Tubesnout 165 3.5 16

Rainbow seaperch 151 3.2 23

Pile perch 142 3.0 15

Copper rockfish 110 2.4 17

Bocaccio 99 2.1 13

Olive/yellowtail rockfish3 72 1.5 13

Giant kelpfish 53 1.1 19

Halfbanded rockfish 44 0.9 6

California lizardfish 27 0.6 3

Painted greenling 25 0.5 13

Blue rockfish 20 0.4 6

Brown rockfish 19 0.4 3

Cabezon 14 0.3 12

C-O Sole 12 0.3 10

Kelp greenling 12 0.3 7

Unidentified kelpfish 10 0.2 7

Calico rockfish 10 0.2 4

Lavender sculpin 8 0.2 6

Kelp bass 7 0.2 4

Unidentified sculpins 6 0.1 5

Blackeye goby 6 0.1 4

Sarcastic fringehead 5 0.1 5

California halibut 5 0.1 4

Lingcod 5 0.1 3

Kelp rockfish 4 0.1 4

Unidentified pipefish 3 0.1 2

Unidentified fish 3 0.1 2

Striped kelpfish 2 >0.1 2

Gopher rockfish 2 >0.1 2

Swell shark 1 >0.1 1

Rock wrasse 1 >0.1 1

Horn shark 1 >0.1 1

Bay ray 1 >0.1 1

Barred sand bass 1 >0.1 1

Sharpnose seaperch 1 >0.1 1

Curlfin sole 1 >0.1 1

Unidentified midshipman 1 >0.1 1

Unidentified ronquil 1 >0.1 1

Grass rockfish 1 >0.1 1

Unidentified perch 1 >0.1 1

Round stingray 1 >0.1 1

Total 4,603

Table 2-4. All fishes observed at bottom depths of 10–11 m and 13–14 m over energized cables, pipe, and natural 

habitat in southern California, 2012–2014. FO = frequency of occurrence (of 38 surveys).
34

Species Number Mean Density Percent 

Abundance FO

Senorita 393 4.3 22.8 23

Unidentified sanddabs 315 3.5 18.3 38

Kelp perch 192 2.1 11.2 19

White seaperch 156 1.7 9.1 18

Unidentified rockfish YOY 129 1.4 7.5 15

Black perch 67 0.7 3.9 20

Vermilion rockfish 62 0.7 3.6 11

Copper rockfish 55 0.6 3.2 11

Shiner perch 52 0.5 3.0 3

Rainbow seaperch 44 0.5 2.6 19

Giant kelpfish 35 0.4 2.0 15

Tubesnout 35 0.4 2.0 5

Bocaccio 28 0.3 1.6 10

California lizardfish 22 0.2 1.3 2

Shortbelly rockfish 20 0.2 1.2 1

Olive/yellowtail rockfish 18 0.2 1.0 10

Halfbanded rockfish 16 0.2 0.9 6

Painted greenling 12 0.1 0.7 9

Blue rockfish 10 0.1 0.6 4

Pile perch 9 0.1 0.5 6

C-O sole 6 0.1 0.3 5

Calico rockfish 6 0.1 0.3 3

Kelp bass 5 0.1 0.3 2

Sarcastic fringehead 3 >0.1 0.2 3

Cabezon 3 >0.1 0.2 3

Lavender sculpin 3 >0.1 0.2 2

Unidentified fishes 3 >0.1 0.2 2

Unidentified kelpfishes 2 >0.1 0.1 2

Kelp greenling 2 >0.1 0.1 2

Lingcod 2 >0.1 0.1 2

Kelp rockfish 2 >0.1 0.1 2

Rock wrasse 1 >0.1 0.1 1

Barred sand bass 1 >0.1 0.1 1

Brown rockfish 1 >0.1 0.1 1

Gopher rockfish 1 >0.1 0.1 1

Unidentified pipefish 1 >0.1 0.1 1

Round stingray 1 >0.1 0.1 1

Total 1,713 18.9

Table 2-5. Fishes observed at bottom depths of 10–11 m and 13–14 m over energized cables in southern California, 

2012–2014. Density is in fish per 100 m3

. FO = frequency of occurrence (of 38 surveys).
35

Table 2-6. Fishes observed at bottom depths of 10–11 m and 13–14 m over a pipe in southern California, 2012–2014. 

Density is in fish per 100 m3. FO = frequency of occurrence (of 38 surveys).

Species Number Mean Density Percent

Abundance FO

Senorita 408 4.5 22.3 20

Unidentified rockfish YOY 195 2.1 10.7 21

Vermilion rockfish 164 1.8 9.0 12

Pile perch 130 1.4 7.1 11

Black perch 114 1.3 6.2 22

Unidentified sanddabs 110 1.2 6.0 31

Rainbow seaperch 87 1.0 4.8 21

White seaperch 86 0.9 4.7 16

Kelp perch 81 0.9 4.4 13

Bocaccio 67 0.7 3.7 5

Copper rockfish 52 0.6 2.8 16

Shortbelly rockfish 50 0.6 2.7 1

Olive/yellowtail rockfish 43 0.5 2.4 8

Halfbanded rockfish 28 0.3 1.5 5

Tubesnout 20 0.2 1.1 9

Brown rockfish 18 0.2 1.0 3

Giant kelpfish 16 0.2 0.9 10

Painted greenling 13 0.1 0.7 8

Shiner perch 12 0.1 0.7 3

Cabezon 10 0.1 0.5 9

Kelp greenling 10 0.1 0.5 6

Blue rockfish 10 0.1 0.5 3

Unidentified kelpfish 8 0.1 0.4 6

Unidentified sculpins 6 0.1 0.3 5

Blackeye goby 6 0.1 0.3 4

Lavender sculpin 4 >0.1 0.2 3

Calico rockfish 4 >0.1 0.2 2

Striped kelpfish 2 >0.1 0.1 2

Sarcastic fringehead 2 >0.1 0.1 2

Kelp bass 2 >0.1 0.1 2

California halibut 2 >0.1 0.1 2

C-O sole 2 >0.1 0.1 2

Kelp rockfish 2 >0.1 0.1 2

Swell shark 1 >0.1 0.1 1

Horn shark 1 >0.1 0.1 1

Unidentified midshipman 1 >0.1 0.1 1

Unidentified ronquil 1 >0.1 0.1 1

Gopher rockfish 1 >0.1 0.1 1

Grass rockfish 1 >0.1 0.1 1

Unidentified pipefish 1 >0.1 0.1 1

Total 1,771 20.1
36

Species Number Mean

Density

Percent

Abundance FO

Shiner perch 270 3.0 24.1 5

Unidentified sanddabs 222 2.4 19.8 37

Senorita 175 1.9 15.6 19

Shortbelly rockfish 120 1.3 10.7 1

White seaperch 110 1.2 9.8 17

Tubesnout 110 1.2 9.8 8

Vermilion rockfish 29 0.3 2.6 5

Rainbow seaperch 20 0.2 1.8 8

Olive/yellowtail rockfish 11 0.1 1.0 5

Unidentified rockfish YOY 7 0.1 0.6 7

Black perch 6 0.1 0.5 3

Kelp perch 5 0.1 0.4 3

California lizardfish 5 0.1 0.4 2

C-O sole 4 >0.1 0.4 3

Bocaccio 4 >0.1 0.4 2

Pile perch 3 >0.1 0.3 3

Copper rockfish 3 >0.1 0.3 3

Lingcod 3 >0.1 0.3 2

California halibut 3 >0.1 0.3 2

Giant kelpfish 2 >0.1 0.2 2

Lavender sculpin 1 >0.1 0.1 1

Bat ray 1 >0.1 0.1 1

Sharpnose seaperch 1 >0.1 0.1 1

Curlfin sole 1 >0.1 0.1 1

Cabezon 1 >0.1 0.1 1

Unidentified pipefish 1 >0.1 0.1 1

Unidentified perch 1 >0.1 0.1 1

Total 1,119 12.3

Table 2-7. Fishes observed at bottom depths of 10–11 m and 13–14 m over natural habitat in southern California, 

2012–2014. Density is in fish per 100 m3. FO = frequency of occurrence (of 38 surveys).
37

Cables v Pipe

N KS p

3,484 0.053 <0.0001*

Cables v Natural Habitat

N KS p

2,832 0.147 <0.0001*

Pipe v Natural Habitat

N KS P

2,890 0.117 <0.0001*

*Significant at p<.01

Table 2- 8. Comparisons of the size frequency distributions of fishes observed at bottom depths of 10–11 m and 13–14 

m over energized cables, pipe, and natural habitat in southern California, 2012–2014 using the Kolmogorov Smirnov 

Two-Sample Test.
38

Table 2-9. Abundance comparisons of the top 15 fish species among the three survey habitats. Analysis excludes survey 

dates when species or species groups were absent. All surveys included six transects: shallower and deeper transects 

along pipe, energized cables, and natural habitat. One-way ANOVA or t-test and Tukey HSD multiple comparison tests 

were used when data was homoscedastic. Welch’s ANOVA or Mann-Whitney test and Wilcoxon method for multiple 

comparisons were used when variances were unequal. * = significance at 0.05 or less. NH = Natural Habitat.

Species All Three

Habitats

Pipe v

Cable

NH v

Cable

NH v

Pipe

Senorita 0.03* 0.49 0.03* 0.20

Unidentified sanddabs <0.01* <0.01* 0.49 <0.01*

White seaperch 0.19

Shiner perch 0.16

Unidentified rockfish YOY <0.01* 0.10* <0.01* <0.01*

Kelp perch <0.01* 0.13 <0.01* <0.01

Vermilion rockfish -0.16

Black perch <0.01* 0.03* <0.01* <0.01*

Tubesnout 0.55

Rainbow seaperch <0.01* 0.11 0.01* <0.01

Pile perch 0.02 0.06 0.27 <0.01

Bocaccio 0.03* 0.21 <0.01* 0.21

Olive/yellowtail rockfish 0.21

Giant kelpfish <0.01* 0.06 <0.01* <0.01*

Copper rockfish <0.01* 0.37 <0.02* <0.01*
39

Common Name Scientific Name Number Density Percent 

Abundance %FO

Bat star Patiria miniata 244 1.1 29.7 50.6%

Pisaster sea stars Pisaster spp. 167 0.8 20.3 34.4%

Purple urchin Strongylocentrotus 

purpuratus 100 0.5 12.2 0.6%

California sea hare Aplysia californica 63 0.3 7.7 18.3%

Comb sand star Astropecten armatus 51 0.2 6.2 16.1%

Kellet's whelk Kelletia kelletii 48 0.2 5.8 12.8%

Sea cucumbers Parastichopus sp. 23 0.1 2.8 9.4%

Rock crabs Metacarcinus sp. 

and Cancer sp. 22 0.1 2.7 8.3%

Kelp crab Pugettia spp. 21 0.1 2.6 7.8%

California market squid eggs Loligo opalescens 20 0.1 2.4 0.6%

Sheep or masking crabs Loxorhynchus spp. 19 0.1 2.3 9.4%

Sand dollars Dendraster excentricus 19 0.1 2.3 4.4%

Octopuses Octopus spp. 12 0.1 1.5 5.6%

Graceful crab Metacarcinus gracilis 5 <0.05 0.6 1.7%

Leather star Dermasterias imbricata 4 <0.05 0.5 1.1%

Giant keyhole limpet Megathura crenulata 2 <0.05 0.2 1.1%

California spiny lobster Panulirus interruptus 1 <0.05 0.1 0.6%

Sunflower star Pycnopodia helianthoides 1 <0.05 0.1 0.6%

Total 822 3.8

Table 2-10. Invertebrates observed at bottom depths of 10–11 m and 13–14 m over energized cables, pipe, and natural 

habitat in southern California, 2012–2014. Density is in fish per 100 m3. FO = frequency of occurrence (of 30 surveys).
40

Bat start

 sea star Pisaster

Purple urchin

California sea hare

Comb sand star

Kellet’s whelk

Sea cucumber

Rock crabs

Kelp crabs

California market squid eggs

Sand dollar

Sheep or masking crab

Octopus

Graceful crab

Leather star

Giant keyhole limpet

California spiny lobster

Sunflower star

CABLES

Number 37 39 0 18 8 12 1 16 9 0 3 4 3 2 3 0 1 1

Density 0.51 0.54 0.00 0.25 0.11 0.17 0.01 0.22 0.13 0.00 0.04 0.06 0.04 0.03 0.04 0.00 0.01 0.01

FO 35% 30% 0% 22% 12% 10% 2% 17% 10% 0% 3% 7% 3% 2% 2% 0% 2% 2%

PIPE

Number 89 112 100 43 12 14 21 3 8 20 1 7 8 2 0 2 0 0

Density 1.24 1.56 1.39 0.60 0.17 0.19 0.29 0.04 0.11 0.28 0.01 0.10 0.11 0.03 0.00 0.03 0.00 0.00

FO 55% 53% 2% 30% 17% 8% 25% 5% 8% 2% 2% 12% 12% 2% 0% 3% 0% 0%

NATURAL HABITAT

Number 118 16 0 2 31 22 1 3 4 0 15 8 1 1 1 0 0 0

Density 1.64 0.22 0.00 0.03 0.43 0.31 0.01 0.04 0.06 0.00 0.21 0.11 0.01 0.01 0.01 0.00 0.00 0.00

FO 62% 20% 0% 3% 20% 20% 2% 3% 5% 0% 8% 10% 2% 2% 2% 0% 0% 0%

Table 2-11. Invertebrates observed at bottom depths of 10–11 m and 13–14 m over energized cables, pipe, and natural habitat, by habitat, in southern California, 2012–2014. Density is in fish per 100 m3. FO = frequency of occurrence (of 30 surveys).
41

Species Number

of Surveys

Number

of Transects Habitats Pipe vCable

NH v

Cable

NH v

Pipe

Pisaster sea stars 23 138 <0.0001* 0.0006* 0.1332 <0.0001*

Bat star 28 168 <0.0001* 0.0043* 0.0001* 0.2356

Comb sand star 12 72 0.0980

California sea hare 21 126 <0.0001* 0.1822 0.0016* <0.0001*

Kellet's whelk 12 72 0.2391

Sea cucumbers 11 66 <0.0001* <0.0001* 1.0000 <0.0001*

Rock crabs 12 72 0.0358* 0.0195* 0.0101* 0.6971

Table 2-12. Habitat comparisons for most common invertebrates observed at bottom depths of 10–11 m and 13–14 

m over energized cables, pipe, and natural habitat in southern California, 2012–2014. One-way ANOVA or t-test and 

Tukey HSD multiple comparison tests were used when data was homoscedastic. Welch’s ANOVA or Mann-Whitney 

test and Wilcoxon method for multiple comparisons were used when variances were unequal. NH = natural habitat.
42

Species Number %FO

Zostera marina 43,072 100

Pterygophora californica 18,175 100

Cystoseira spp. 8,456 100

Laminaria spp. 3,110 100

Macrocystis pyrifera 186 34

Total 72,999

Table 2-13. All plants observed at bottom depths of 10–11 m and 13–14 m over energized cables, pipe, and natural 

habitat in southern California, 2012–2014. FO = frequency of occurrence (of 38 surveys).
43

Habitat Zostera marina Pterygophora 

californica Cystoseira spp. Laminaria spp. Macrocystis pyrifera

Cables

Number 1,182 17,193 1,232 1,220 156

FO 22 38 36 23 6

Pipe

Number 2 982 7,224 1,890 30

FO 4 20 38 24 5

Natural Habitat

Number 41,888 0 0 0 0

FO 38 0 0 0 0

Table 2-14. Numbers and frequency of occurrence of plants observed, by habitat type, at bottom depths of 10–11 m 

and 13–14 m over energized cables, pipe, and natural habitat in southern California, 2012–2014. FO = frequency of 

occurrence (of 38 surveys).
44

Chapter 3. Offshore 

Abstrac

We conducted surveys of energized and unenergized cables and of the nearby sea floor during 2012 (6–9 

October), 2013 (3–5 October) and 2014 (23–25 October) at depths between 76 and 213 m. During 2012, only 

the east side of each cable was surveyed, while in 2013 and 2014 we surveyed both sides of the cables at similar 

depths. All natural habitat surveys were conducted between 100 and about 500 m from the nearest cable. 

In 2012, we measured the EMF levels at three distances from energized Cable A. These measurements were 

taken at four locations along the cable (at bottom depths of 108 m, 112 m, 135 m, and 158 m). At all four 

locations, EMF levels dropped off precipitously with distance from the cable and, at one meter from the cable, 

approached background levels at three of the four locations. 

With one exception (Cable C1 was not measured in 2013), in each year we measured the EMF levels at each 

cable (A, B, C, and C1) and at the sea floor away from these cables. In all years, Cable A was energized and this 

cable formed the basis of our energized cable surveys. In all years Cable C was unenergized and Cable B was 

energized in 2012 and 2014, but unenergized in 2013. Cable C1 was unenergized in 2012 and energized in 

2014. In general, field strengths on the energized cables were around 100 μT, while those on the unenergized 

cables were very low and near background (sea floor) levels.

Fishes

We found that fish species communities were structured by depth more so than by habitat type (Global 

R=0.176, p=0.001). There was no statistical difference between the fish assemblages along the energized 

and unenergized cables. The natural habitat community statistically differed from both the energized cable 

and unenergized cable communities. Within species (or in several cases species-groups) that formed at least 

one percent of the fishes observed, we found no differences in densities between energized and unenergized 

cables. We did find differences based on cable side (shortspine combfish densities were higher on the west 

side of cables), depth strata (stripetail rockfish, unidentified poachers, shortspine combfish, greenstriped 

rockfish, lingcod, and unidentified eelpouts), and year (halfbanded rockfish, stripetail rockfish, and lingcod).

Total fish densities were significantly higher around the cables than over the natural habitat. Among the more 

important species, densities of halfbanded, stripetail, and greenstriped rockfishes, shortspine combfish, and 

lingcod were higher at the cables and eelpouts were found at higher densities over natural habitat. There 

were no significant differences in the densities of unidentified sanddabs and unidentified poachers. There 

were very slight, but statistically significant, differences in both mean lengths and size distributions of fishes 

among the three study habitats as fishes at the unenergized cables tended to be slightly larger (mean = 14.8 

cm) than those at both natural habitats (mean = 13.7 cm) and energized cables (mean = 13.0 cm).

Over all habitats we observed 9,675 individuals of at least 41 species. Dominant species included halfbanded, 

stripetail, and greenstriped rockfishes, and lingcod, and unidentified flatfishes, poachers, and combfishes. 

Energized cables: In the vicinity of the energized cables, we observed at least 33 species of fishes, comprising 

4,455 individuals. Halfbanded rockfish dominated this habitat, comprising 56% of all fishes observed and 

present during 82.3% of the transects. Other important species or species groups included unidentified 

flatfishes and poachers, stripetail and shortspine combfish. Unenergized cables: Similar to the fish assemblage 

found around energized cables, there were at least 35 fish species in proximity to the unenergized cables 

and 3,691 individuals. As with the energized cables, halfbanded rockfish were by far the most abundant 
45

species, comprising 37.4% of all fish observed. Other important species included stripetail and greenstriped 

rockfishes and unidentified flatfishes, poachers, and combfishes. Natural habitats: Fewest species (at least 23) 

and fishes (1,529) were observed on the natural habitats. Here, unidentified flatfishes, eelpouts, poachers, 

combfishes, sanddabs and halfbanded rockfish predominated. 

Invertebrates

The structure of the invertebrate communities living around energized and unenergized cables and natural 

habitats was similar to that of fishes. We found that invertebrate communities were structured by habitat 

type and depth. Similar to the fishes, there was no statistical difference between the invertebrate assemblages 

along the energized and unenergized cables. The natural habitat community of invertebrates strongly 

differed from the energized cable and unenergized cable communities.

To determine if there were significant differences in species densities between energized and unenergized 

cables, we compared the densities of those important species that comprised at least 1% of individuals 

observed in this study in the same way as for fishes. We did note slight but statistically significant differences 

in densities for only two of nine of the most abundant species. Sand star and black crinoid densities differed 

between unenergized and energized cables [sand star greater at unenergized cables, 4/1/m3

 v 2.7 m3, and 

black crinoid at energized cables, 1.7/m3

 v 0.3/m3]. Three species, thin sea pen, red octopus, and white 

sea urchin differed between cable sides. Seven species, white-plumed anemone, spot prawn, thin sea pen, 

California sea cucumber, red octopus, unidentified Urticina anemone, and black crinoid exhibited bottom 

depth differences. Densities of two species, thin sea pen and sand star, varied among years. 

A number of species were more abundant around the cables than over the natural habitats. Important 

species that were more abundant around cables were white-plumed anemone, spot prawn, thin sea pens, 

California sea cucumber, sand star, and unidentified Urticina anemone. Red octopus and white sea urchin 

were denser over natural habitats and densities of black crinoid did not differ between the two habitats.

Over all habitats, we observed a total of 30,523 invertebrates of at least 43 invertebrate species. The whiteplumed anemone was by far the most abundant animal and comprised 43.4% of all invertebrates recorded. 

Spot prawns, thin sea pens, California sea cucumbers, sand stars, and the red octopuses were also found at 

relatively high densities. Energized cables: We observed 13,388 individuals, of at least 36 species, living on or 

near the energized cables. White-plumed anemones, thin sea pens and spot prawns were the species found in 

highest densities, forming in aggregate 79.7% of all invertebrates observed. California sea cucumbers, sand 

stars, red octopuses, black crinoids, and Urticina anemones were also common. Unenergized cables: At least 

35 species and 14,619 individuals were observed along the unenergized cables. Three species, white-plumed 

anemones, spot prawns, and thin sea pens, were by far the most dense, in aggregate forming 79.2% of all 

invertebrates surveyed. California sea cucumbers, sand stars, red octopus, unidentified Urticina anemones, 

and serpulid worms were also characteristic of this habitat. Natural habitats: We observed the fewest number 

of species (a minimum of 27) and individuals (2,516) over the natural habitat. Thin sea pens, red octopuses, 

white sea urchins and sand stars dominated this habitat, along with smaller numbers of white-plumed 

anemones, fragile pink urchins, California sea cucumbers, and sea slugs.

Regarding the specific objectives of this study: 

1) The differences among fish and invertebrate communities associated with energized and unenergized 

cable habitat and those communities in soft seafloor habitats lacking cables.
46

We did not observe any significant differences in the fish communities living around energized and 

unenergized cables and natural habitats. A very slight, and likely biologically insignificant, difference in 

mean sizes was observed as fishes at unenergized cables were marginally larger than those around energized 

ones. Overall species diversity and the densities of the most important fish species (define as comprising at 

least 1% of all fishes observed) were higher at the cables than at the natural habitats. This is likely reflective 

of the more complex habitats afforded by the cables than the primarily soft substrata natural habitats.

Similar to the fish communities, the invertebrate assemblages living around energized and unenergized 

cables and natural habitats were similar to one another and variability between these communities was 

primarily driven by sea floor depth. Among the three habitat types, there were some statistically significant 

differences in densities for all nine of the most abundant species. These differences included: 1) two species, 

sand star and black crinoid, whose densities differed between energized and unenergized cables, 2) three 

species, thin sea pen, red octopus, and white sea urchin which differed between cable sides, 3) seven species, 

white-plumed anemone, spot prawn, thin sea pen, California sea cucumber, red octopus, unidentified 

Urticina anemone, and black crinoid that exhibited bottom depth differences, and 4) two species, thin sea 

pen and sand star, whose densities varied among years. Sand star densities were greater at unenergized 

cables, 4/1/m3

 v 2.7 m3, and black crinoid densities were greater at energized cables, 1.7/m3 v 0.3/m3. 

2) Whether electro-sensitive species that are regionally important, such as sharks and rays, respond (via 

either attraction or repulsion) to the EMFs of an in situ power transmission cable.

We observed very few individuals of electro-sensitive species on the energized or unenergized cables or on 

the natural habitats. Only five ratfish (three at the energized cables and two on the unenergized ones) and 

one California skate (at the unenergized cable) were noted. Thus, we found no compelling evidence that the 

EMF produced by the energized power cables in this study were either attracting or repelling these fishes. 

3) The strength, spatial extent, and variability of EMFs along both energized and unenergized cables.

The EMFs produced by the energized cables were similar both over the three years of the study and along the 

cables. EMF strength dissipated relatively quickly with distance from the cable and approached background 

levels at about one meter from the cable. The EMF at unenergized cables was similar to that found at the 

natural habitats.

4) The potential effectiveness of the commonly proposed mitigation of cable burial.

Given the rapidity with which the EMF produced by the energized cables diminishes and the lack of response 

to that EMF by the fishes and invertebrates in this study, cable burial would not appear necessary strictly for 

biological reasons. In this and similar cases, cable burial, at sufficient depth, would be an adequate tool to 

prevent EMF emissions from being present at the seafloor.
47

Method

Our surveys of the offshore marine communities were conducted off the coast of Las Flores Canyon, 

southern California (34°27.6 ́N, 120°02.7 ́W) (Figure 3-1). At this site there are four, variously energized and 

unenergized, 8” diameter submarine power cables providing power to three offshore oil platforms. Surveys 

were conducted aboard the research submersibles Dual DeepWorker (2012 and 2014) and DeepWorker (2013). 

These submarines are 7.2 m in length and have a maximum operating depth of 610 m. The DeepWorker 

accommodates a pilot and the Dual DeepWorker accommodates both a pilot and an observer. Dives were 

made in September and October, during daylight hours. 

We conducted belt transects along cables and on the nearby sea floor. These were documented with an 

externally mounted high-definition video camera positioned on the starboard bow of the submersible. All 

transects were 2-m wide and a set of lasers was used to measure transect width. A green and a red laser were 

set at an angle such that they intersected one another at a distance 2 m away from the submersible. The 

submersible followed a path parallel to the cable such that the intersection of the lasers landed on the cable. 

For off-cable (natural sea floor) transects, the crossing lasers were used to delineate the outside edge of each 

transect with the submarine continuing along a straight path along a compass heading for the duration of 

that transect.

During 2012 and 2014, and while in the submersible, the observer recorded into the microphone of a video 

recorder the species (to lowest possible taxon) of every fish observed within the transect boundary. The 

observer also estimated the total length (cm) of these fishes using reference light points from two parallel 

lasers installed 20 cm apart on either side of the external video camera. Comments were also made regarding 

general habitat and notable invertebrates. In 2013, when there was only a pilot aboard the submersible, we 

took data on fishes from the high definition video after returning to the laboratory. 

In the laboratory, each video-recorded transect was reviewed and each fish again identified to the lowest 

possible taxa and its total length (estimated to the nearest 5 cm) recorded in an Access database. In a separate 

viewing of these videos, large invertebrates within the dimensions of the transect were surveyed. Any 

bottom-dwelling individual invertebrate with at least one dimension of ≥5 cm was included. The minimum 

dimension of 5 cm was selected because it was the size that could reliably be seen and identified. A few 

invertebrates, such as brittle stars, which were mostly buried could not be distinguished as individuals and 

were not counted. Invertebrates were identified to the lowest possible taxon. Transect length for the cable 

surveys was measured using an existing map of the cables and positions from a Ultra-Short Baseline (USBL) 

tracking system on the submersible. Navigation fixes were received from a Thales GeoPacific Winfrog ORE 

Trackpoint 2 USBL system at two-second intervals. Using the start and end points, and general path of 

the submarine from the USBL tracking system, the length of the submersible’s path along the cable was 

measured using a straight-line ruler tool in ArcGIS. For the off-cable (natural sea floor) sites, the tracking 

system points were smoothed using a 9-point moving boxcar average and then plotted. Then the end-to-end 

straight-line distance was measured using a ruler tool in ArcGIS for each straight segment of a transect and 

segment lengths were totaled to obtain transect length. Most transects were only one straight segment. This 

method was found to be more accurate than calculating the distance between smoothed points, as the two 

methods were compared using the data from the cable surveys along a known path. 
48

Measuring the Electromagnetic Field 

We measured the electromagnetic field (EMF) emitted by the cables and the natural sea floor sites. In 2012, 

EMF readings were taken at distances of 1 m, 0.5 m, and 0 m from each cable. A Y-shaped measuring stick 

was attached to the EMF reader on the submersible’s mechanical arm in order to ensure a perpendicular 

measurement from the cable (Figure 3-2). For each reading, the device was held in position until the 

readings stabilized (within approximately 1% of one another) and then the next three readings were taken 

and averaged. For natural habitat sites, readings were taken in a similar manner, but in a single position with 

the device touching the bottom. In 2013 and 2014 readings were taken on all cables, and on mud, but only 

at the 0 m distance.

Statistical Analysis 

We used Primer v6.1.13 (Primer-E Ltd, 2009) to examine the biological assemblage data in relation to 

the type of habitat (energized cable, unenergized cable, and seafloor without cable) and bottom depth. 

Density was transformed to log[(number per 100m3

)+1] for the multivariate analyses. Bray-Curtis 

similarity coefficients were calculated to quantify the resemblance between transect samples and similarity 

matrices were generated for fish and invertebrates, separately. Natural groupings of samples were examined 

using hierarchical clustering with the group average linkage option and multidimensional scaling (MDS) 

ordination. 

To test the null hypothesis that there are no assemblage differences among the two cable states and natural 

habitats (factor A) and depth (factor B) we used a two-way crossed analysis of similarity (ANOSIM), a 

nonparametric permutation procedure that operates on the resemblance matrix (Primer-E Ltd, 2009; 

Clarke and Gorley, 2006). Transects were divided into four depth stratum groups based on the clustering 

and MDS representations. The ANOSIM test statistic R ranges between 0 (approximately) and 1 and is very 

close to 0 if the null hypothesis is true with similarities between and within groups the same on average. The 

R statistic is a useful comparative measure of the degree of separation between groups. R values close to 1 are 

indicative of complete separation between groups. The global ANOSIM test indicates an overall difference 

among groups, and pairwise comparison tests using ANOSIM identifies the groups that differ from one 

another (p<0.05).

We used a generalized linear model (GLM) approach to test if cable state (energized v unenergized), 

controlling for other factors, affected the abundance of individual taxa of fishes and invertebrates. The 

GLM, with a normal distribution response and identity link function, included four factors: cable state, 

side of cable (west and east nested in cable state), bottom depth (stratum groups 1, 2, 3, and 4), and year 

(2012, 2013, 2014). The model, analogous to a multiple linear regression, was fit to transformed density 

data, log[(number per 100m3

)+1], by the Firth bias-adjusted maximum likelihood estimation method. A 

likelihood-ratio Chi-square test evaluated the hypothesis that all the model parameters in the whole model 

were zero. If the whole model was statistically different from the intercept model (p<0.05), then effect tests 

were used to identify which of the four factors had a significant effect on a taxon’s abundance (p<0.05). 

Analyses were performed in JMP (SAS, 2015; Fox, 2014).

The same GLM approach was used to test if habitat type (cable v natural) affected the abundance of individual 

taxa controlling for the effects of bottom depth and year. In order to avoid including transects from both the 

west and east side of the cable within any given depth level and year in a single model, we used transects on 

the east side of the cable or on the west side if the east side was not surveyed. If side of cable had a significant 

effect on abundance, then we would evaluate models using transects from each side of the cable separately. 
49

Results

We conducted surveys of energized and unenergized cables and of the nearby sea floor during 2012 (6–9 

October), 2013 (3–5 October) and 2014 (23–25 October) (Table 3-1, Figures 3-3, 3-4, 3-5) at depths between 

76 and 213 m (Table 3-1). During 2012, only the east side of each cable was surveyed. However, out of 

concern that there might be differences in species assemblages between the sides of cables, in 2013 and 2014 

we surveyed both sides of the cables at similar depths. All natural habitat surveys were conducted between 

100 and about 500 m from the nearest cable. 

Note that for some analyses we divided the transect depths into four strata based on species groupings 

determined by MDS analyses of fish and invertebrate communities. These are defined as: Stratum 1 (transect 

categories1–8 = 76–107 m), Stratum 2 (transect categories 9–10 = 104–144 m), Stratum 3 (transect categories 

11–13 = 137–180 m) and Stratum 4 (14–17 = 175–213 m) (Table 3-1).

EMF Levels

On 6 October 2012, we measured the EMF levels at three distances from energized Cable A. These 

measurements were taken at four locations along the cable (at bottom depths of 108 m, 112 m, 135 m, and 

158 m). At all four locations, EMF levels dropped off precipitously with distance from the cable and, at one 

meter from the cable, approached background levels at three of the four locations (Table 3-2). This sharp 

drop-off was similar to that found in the nearshore part of this cable (Love et al. 2015).

With one exception (Cable C1 was not measured in 2013), in each year we measured the EMF levels at each 

cable (A, B, C, and C1) and at the sea floor away from these cables (Table 3-3). In all years, Cable A was 

energized and this cable formed the basis of our energized cable surveys. In all years Cable C was unenergized 

and Cable B was energized in 2012 and 2014, but unenergized in 2013. Cable C1 was unenergized in 2012 

and energized in 2014. In general, field strengths on the energized cables were around 100 μT, while those on 

the unenergized cables were very low and near background (sea floor) levels (Table 3-3).

Fishes

We found that fish species communities were structured by depth (Global R=0.553, p=0.001) more so 

than by habitat type (Global R=0.176, p=0.001) (Figure 3-6). There was no statistical difference between 

the fish assemblages along the energized and unenergized cables (R=-0.055, p=0.87). The natural habitat 

community statistically differed from the energized cable (R=0.304, p=0.003) and unenergized cable 

communities (R=0.341, p=0.001). 

We used a GLM approach to test for the effects on fish density of 1) cable state (energized or unenergized), 

2) side of cable (nested in cable type), 3) depth strata, and 4) year (Table 3-4). Within species (or in several 

cases species-groups) that formed at least one percent of the fishes observed, we found no differences in 

densities between energized and unenergized cables. We did find differences based on cable side (shortspine 

combfish densities were higher on the west side of cables, two-tail t test, t=2,582, df 61, p=0.012), depth 

strata (stripetail rockfish, unidentified poachers, shortspine combfish, greenstriped rockfish, lingcod, and 

unidentified eelpouts), and year (halfbanded rockfish, stripetail rockfish, and lingcod).

Total fish densities were significantly higher around the cables than over the natural habitat (Figure 

3-7). Among the more important species, densities of halfbanded, stripetail, and greenstriped rockfishes, 

shortspine combfish, and lingcod were higher at the cables and eelpouts were found at higher densities over 

natural habitat (Figure 3-8). There were no significant differences in the densities of unidentified sanddabs 
50

and unidentified poachers. There were very slight, but statistically significant, differences in both mean 

lengths and size distributions of fishes among the three study habitats (Table 3-5, Figure 3-9) as fishes at the 

unenergized cables tended to be slightly larger (mean = 14.8 cm) than those at both natural habitats (mean 

= 13.7 cm) and energized cables (mean = 13.0 cm). 

Over all habitats we observed 9,675 individuals of at least 41 species (Tables 3-6, 3-7). Dominant species 

included halfbanded, stripetail, and greenstriped rockfishes, and lingcod, and unidentified flatfishes, 

poachers, and combfishes. Energized cables: In the vicinity of the energized cables, we observed at least 33 

species of fishes, comprising 4,455 individuals (Table 3-8). Halfbanded rockfish dominated this habitat, 

comprising 56% of all fishes observed and present during 82.3% of the transects. Other important species or 

species groups included unidentified flatfishes and poachers, stripetail and shortspine combfish. Unenergized 

cables: Similar to the fish assemblage found around energized cables, there were at least 35 fish species 

in proximity to the unenergized cables (Table 3-9) and 3,691 individuals. As with the energized cables, 

halfbanded rockfish were by far the most abundant species, comprising 37.4% of all fish observed. Other 

important species included stripetail and greenstriped rockfishes and unidentified flatfishes, poachers, and 

combfishes. Natural habitats: Fewest species (at least 23) and fishes (1,529) were observed on the natural 

habitats (Table 3-10). Here, unidentified flatfishes, eelpouts, poachers, combfishes, sanddabs and halfbanded 

rockfish predominated. 

Invertebrates

The structure of the invertebrate communities living around energized and unenergized cables and natural 

habitats was similar to that of fishes (Figure 3-10). We found that invertebrate communities were structured 

by habitat type (Global R=0.596, p=0.001) and depth (Global R=0.481, p=0.001). Similar to the fishes, 

there was no statistical difference between the invertebrate assemblages along the energized and unenergized 

cables (R=0.039, p=0.218). The natural habitat community of invertebrates strongly differed from the 

energized cable (R=0.846, p=0.001) and unenergized cable communities (R=0.751, p=0.001).

To determine if there were significant differences in species densities between energized and unenergized 

cables, we compared the densities of those important species that comprised at least 1% of individuals 

observed in this study in the same way as for fishes. We did note slight but statistically significant differences 

in densities for only two of nine of the most abundant species (Table 3-11). Sand star and black crinoid 

densities differed between unenergized and energized cables [sand star greater at unenergized cables, 4/1/

m3 v 2.7 m3

, and black crinoid at energized cables, 1.7/m3 v 0.3/m3]. Three species, thin sea pen, red octopus, 

and white sea urchin differed between cable sides. Seven species, white-plumed anemone, spot prawn, thin 

sea pen, California sea cucumber, red octopus, unidentified Urticina anemone, and black crinoid exhibited 

bottom depth differences. Densities of two species, thin sea pen and sand star, varied among years. 

A number of species were more abundant around the cables than over the natural habitats. Important 

species that were more abundant around cables were white-plumed anemone, spot prawn, thin sea pens, 

California sea cucumber, sand star, and unidentified Urticina anemone. Red octopus and white sea urchin 

were denser over natural habitats and densities of black crinoid did not differ between the two habitats 

(Figure 3-11).

Over all habitats, we observed a total of 30,523 invertebrates of at least 43 invertebrate species (Tables 

3-12, 3-13). The white-plumed anemone was by far the most abundant animal and comprised 43.4% of 

all invertebrates recorded. Spot prawns, thin sea pens, California sea cucumbers, sand stars, and the red 

octopuses were also found at relatively high densities. Energized cables: We observed 13,388 individuals, 
51

of at least 36 species, living on or near the energized cables (Table 3-14). White-plumed anemones, thin 

sea pens and spot prawns were the species found in highest densities, forming in aggregate 79.7% of all 

invertebrates observed. California sea cucumbers, sand stars, red octopuses, black crinoids, and Urticina

anemones were also common. Unenergized cables: At least 35 species and 14,619 individuals were observed 

along the unenergized cables (Table 3-15). Three species, white-plumed anemones, spot prawns, and thin 

sea pens, were by far the most dense, in aggregate forming 79.2% of all invertebrates surveyed. California 

sea cucumbers, sand stars, red octopus, unidentified Urticina anemones, and serpulid worms were also 

characteristic of this habitat. Natural habitats: We observed the fewest number of species (a minimum of 27) 

and individuals (2,516) over the natural habitat (Table 3-16). Thin sea pens, red octopuses, white sea urchins 

and sand stars dominated this habitat, along with smaller numbers of white-plumed anemones, fragile pink 

urchins, California sea cucumbers, and sea slugs.

Discussion

The fish communities living around the cables and adjacent natural habitats in this study are typical of 

those found throughout central and southern California on 1) soft substrata, 2) cobble-strewn edges of 

rocky reefs, 3) the low-relief shell mounds around oil and gas platforms, and 4) adjacent to the low-relief 

oil and gas pipelines of southern California (Love et al. 1999, Love and York 2005, Anderson and Yoklavich 

2007). A number of species of rockfishes, in particular, but also flatfishes, combfishes, and eelpouts are 

representative of these habitats. These fishes tend to be solitary rather than schooling (halfbanded rockfish 

are an exception) and benthic rather than water column dwelling. They also tend to reach relatively small 

maximum size. All of these characteristics reflect living in an environment that has no large structures that 

would allow for refuges or point of orientation.

Although we found no evidence that there were differences in fish communities between energized and 

unenergized cables, the abundances of some fishes did vary between cable sides (regardless of whether they 

were energized or not), with depth, and among years. It might be expected that abundances would vary with 

depth, reflective of depth preferences among species, and year, reflecting the patchiness of many species’ 

small-scale distributions. However, the greater abundance of shortspine combfish on the west side of cables 

was unexpected and we have no definitive explanation for it. We have noted that, at times, mud will pile up 

on one side of the cable compared to the other, reflective of bottom current patterns. When this occurs it 

might be argued that sediment grain size differs between the two sides and that combfish are reacting to this 

– perhaps finding higher densities of benthic invertebrate prey on one side over the other. However, when 

we examined those patches where shortspine combfish were most abundant we did not see any obvious 

differences between the sides.

Electro-sensitive fishes were not abundant in the study area; only five ratfish (three at the energized cables 

and two on the unenergized ones) and one California skate (at the unenergized cable) were observed. It 

is important to note that, in the depth ranges we surveyed, both benthic elasmobranchs (sharks, skates, 

and rays) and chimaerids (ratfishes) are common in southern California waters (Love et al. 2009, Love 

2012). However, with the exception of the schooling Pacific dogfish (Squalus suckleyi) and soupfin shark 

(Galeorhinus zyopterus), most of these species live solitary existences and thus it would be unlikely that we 

would have observed large numbers of any of these species (again with the possible exceptions of Pacific 

dogfish and soupfin shark) unless these habitats were somehow attracting these fishes. Thus, specifically, 

because we did not observe high densities of electro-sensitive fishes around energized cables or, on the 

contrary, around the unenergized ones, it might be argued these taxa are neither attracted to, nor repelled 

by, the EMF emitted.
52

Similar to the fish communities, we observed almost no differences in the abundances of important 

invertebrate species between energized and unenergized cables. 

In particular, at these structures we found that the six invertebrate species that were most abundant at 

energized cables (white-plumed anemone, spot prawn, thin sea pen, California sea cucumber, sand star, 

and red octopus) were the most abundant taxa at unenergized cables. Again, as with the fish communities, 

bottom depth was a major driver of variability in the invertebrate communities. And again like the fishes 

we observed, these invertebrate species are very typical of both low-relief and soft substrata sea floors in 

southern and central California (Goddard and Love 2010, Kuhnz et al. 2015). 

The cable habitat harbored many more invertebrate species and numbers than did the natural habitat. It 

is likely that this was due to the cables (hard, although relatively low structures) creating a more complex 

environment than that of the mud that formed most of the natural sea floor. In our cable surveys, we included 

not only the cable but also the sea floor within 2 m of the cable. This methodology allowed us to include not 

only organisms that might preferentially live on hard structure, such as white-plumed anemones, but also 

those dwelling on soft sea floor, such as sea pens. 

As with the fishes, there were invertebrate taxa whose densities were greater on one side of the cable; these 

were red octopus and thin sea pen (Table 3-17). In two taxa, red octopus and thin sea pen, densities were 

significantly higher on the east side of the cables. Densities of red octopus were about twice as high on the 

east side and about nine times higher for thin sea pen. While we do not know why these patterns occurred, 

in the case of sea pens it is known that at least some species are highly sensitive to substratum grain size. 

For instance several species of sea pens in Scottish marine waters are abundant in mud and become rare or, 

ultimately, absent as the amount of gravel increases (Greathead et al. 2015). As noted before, it is possible 

that currents, playing over the cables, can distribute sediments based on grain size, thus leading to coarser 

sediments on one side and finer on the other. Similarly, it is possible that octopus prey were more abundant 

on one side of the cable compared to the other.

Data from the few field studies on the behavior of fishes in the presence of human-induced EMF in 

submarine power cables are, at best, equivocal. Westerberg and Lagenfelt (2008) observed the swimming 

speed of European eel, Anguilla anguilla, passing over a 130 kV AC power cable in the Baltic Sea. They 

found a small effect with eels slowing their swimming speed both when approaching and exiting from the 

cable region. However, there was no statistically significant relationship between the amperage in various 

parts of the cable and swimming speed. Gill et al. (2009) characterized the movements of three species 

of electro-sensitive elasmobranchs, thornback ray (Raja clavata), spurdog (Squalus acanthias), and smallspotted catshark (Scyliorhinus canicula), in enclosed mesocosms off Scotland containing either energized or 

unenergized cables. They found that one of the three species (spotted catshark) tended to be attracted to the 

energized cable compared to the unenergized one while the other two species did not show any differences 

in their responses. Lastly, DONG Energy and Vattenfall (2006) looked at the distribution of fishes in a 

nearshore area of the North Sea before and after the energizing of a submarine power cable transmitting 

energy from an offshore wind farm. They found evidence that the migrations of four species Baltic herring 

(Clupea harengus), European eel, Atlantic cod (Gadus morhua), and flounder (Platichthys flesus) appeared 

to be somewhat hindered by an energized cable. 

The most apt comparisons between our findings and those of others are the surveys of fishes and invertebrates 

conducted in Monterey Bay, central California (Kogan et al. 2003, Kuhnz et al. 2011, 2015) on and near a 

power cable extending from land to the Pioneer Seamount, located about 51 km offshore. Note that this cable 
53

was smaller than the cables we studied (3.2 cm versus 20 cm diameter) and carried lower voltages (10 Kv 

versus 35 Kv) and the EMF emitted by the MBARI cable was not measured. 

Using an ROV, the MBARI researchers surveyed the organisms living near or on the cable and those living on 

natural habitat control sites 50 m away using 100 m-long transects positioned every 5 km. Surveys were first 

conducted before the cable was first energized in 2008 (Kogan et al. 2003, Kuhnz et al. 2011), with subsequent 

post-energized surveys in 2010 (Kuhnz et al. 2011) and again in 2014–2015 (Kuhnz et al. (2015). The major 

findings of the latest study (that also summarize the 2010 surveys) (Kuhnz et al. 2015) were that: 

1) The abundances of most animals observed did not differ between the area over the cable route and 

50 m away.

2) The overall faunal communities did not differ between the cable and control site. Thus, the cable had 

little or no detectable effect on the distribution and abundance of either faunal assemblages.

3) The faunal communities did not differ between sampling years.

4) Faunal assemblages did vary with depth.

5) The abundance and distribution of fauna appears to be most closely linked to natural variation rather 

than to either the presence of the cable or whether it is energized.

6) Although electro-receptive species, such as skates and ratfishes, were observed the densities of these 

animals were no higher near the energized cable than at the control site.

Overall, cnidarians (sea pens and anemones) were most important and comprised 47% of all individuals 

observed and echinoderms (sea stars and urchins primarily) were second-most important at 42%. Among 

fishes, flatfishes and rockfishes were the dominant groups. 

In several ways, our findings mirror those of Kuhnz et al. (2015). First, and most importantly, we also found 

little evidence that energized cables either attract or repel the marine organisms living in their vicinity. This 

is particularly striking as the cables in our study were both physically larger in diameter and carried more 

voltage (and thus likely also created greater EMF). In addition, the same group of fishes and invertebrates that 

were characteristic of the Kuhnz et al. study, also dominated the habitats in ours. Among fishes, rockfishes 

and flatfishes also dominated our sites as did, among invertebrates, cnidarians and echinoderms. And among 

the more striking similarities, white-plumed anemones were about 40 times more abundant on the cables 

than the natural habitat in Monterey Bay and 23 times more abundant in our study. The greatest difference 

between the studies was that spot prawns were quite abundant around our study cables and almost absent 

from the Monterey sites (L. Kuhnz, pers. comm. to M. L.).

We note that an observation by Kuhnz et al. (2011) demonstrates the complexities in distinguishing between 

human-induced and naturally occurring behaviors. In 2008, before the MBARI cable was energized, Kuhnz 

et al. (2011) reported a dense aggregation of longnose skate (Raja rhina) lying on the sea floor primarily 

within 5–10 m of the cable at a bottom depth of 300 m. The unenergized cable at this location was lying on 

rocks and suspended slightly above the sea floor. The authors speculated that “The suspended MARS cable 

very likely produced a weak electromagnetic field as local ocean currents flow through the Earth’s magnetic 

field and around the cable...This is possible even though the cable was not energized during the 2008 video 

survey. We noted that while the cable was taut and 2–10 cm off the seafloor in other areas with topographic 

highs and lows, no other skate aggregations were seen. The combination of topography (small scarps and 
54

sediment depressions unique to this area), natural distribution of the animals, and a mild electrical field may 

have contributed to the aggregation.” It is important to note that after the cable was energized subsequent 

surveys of this location found no aggregations of skates and no aggregations of skates were noted anywhere 

along the energized cable or in the control sites in these subsequent surveys (Kuhnz et al. 2011, 2015). At the 

very least, this presents a cautionary note regarding the interpretation of short-term or one-time surveys. 

Kuhnz et al. (2015) also note that “While there were significant results [differences between cable and 

control site] for Ophiuroids (brittlestars) at the Shelf region, and for Pleuronectiformes (flatfishes) at the 

Neck region, we know that from our general [not affiliated with these surveys] benthic studies that both of 

these groups of animals are highly mobile and form ephemeral aggregations; these results may represent 

natural variability.” We posit that many or perhaps all of the few significant differences we observed between 

taxa at energized and unenergized cables, such as in mean sizes of fishes or densities of several invertebrates, 

may represent natural variability. In any case, we believe it is quite possible that none of these differences are 

biologically significant.

There is a substantial body of research that demonstrates that a number of marine organisms can detect 

naturally occurring EMFs and perhaps utilize this ability for navigation, prey detection, and other functions 

(Normandeau et al. 2011). If this is the case, what, then might explain the lack of response to the humaninduced EMF produced by the submarine power cables in our study? One possible explanation is that marine 

organisms may respond to human-induced EMF differently from those produced in nature. Recent studies 

demonstrate that human-made EMF is inherently different from naturally produced EMF; it is polarized and 

thus more biologically active (Panagopoulos et al. 2015). Thus, it is possible that electro-sensitive organisms 

are able to differentiate between the two types and therefore respond differently to each of these stimuli. 

Regarding the specific objectives of this study: 

1) The differences among fish and invertebrate communities associated with energized and unenergized cable 

habitat and those communities in soft seafloor habitats lacking cables.

We did not observe any significant differences in the fish communities living around energized and 

unenergized cables and natural habitats. A very slight, and likely biologically insignificant, difference in 

mean sizes was observed as fishes at unenergized cables were marginally larger than those around energized 

ones. Overall species diversity and the densities of the most important fish species (define as comprising at 

least 1% of all fishes observed) were higher at the cables than at the natural habitats. This is likely reflective 

of the more complex habitats afforded by the cables than the primarily soft substrata natural habitats. 

Similar to the fish communities, the invertebrate assemblages living around energized and unenergized 

cables and natural habitats were similar to one another and variability between these communities was 

primarily driven by sea floor depth. 

Among the three habitat types, there were some statistically significant differences in densities for all nine 

of the most abundant species. These differences included: 1) two species, sand star and black crinoid, whose 

densities differed between energized and unenergized cables, 2) three species, thin sea pen, red octopus, and 

white sea urchin which differed between cable sides, 3) seven species, white-plumed anemone, spot prawn, 

thin sea pen, California sea cucumber, red octopus, unidentified Urticina anemone, and black crinoid that 

exhibited bottom depth differences, and 4) two species, thin sea pen and sand star, whose densities varied 

among years. Sand star densities were greater at unenergized cables, 4/1/m3

 v 2.7 m3, and black crinoid 

densities were greater at energized cables, 1.7/m3

 v 0.3/m3. 
55

2) Whether electro-sensitive species that are regionally important, such as sharks and rays, respond (via 

either attraction or repulsion) to the EMFs of an in situ power transmission cable.

We observed very few individuals of electro-sensitive species on the energized or unenergized cables or on 

the natural habitats. Only five ratfish (three at the energized cables and two on the unenergized ones) and 

one California skate (at the unenergized cable) were noted. Thus, we found no compelling evidence that the 

EMF produced by the energized power cables in this study were either attracting or repelling these fishes. 

3) The strength, spatial extent, and variability of EMFs along both energized and unenergized cables.

The EMFs produced by the energized cables were similar both over the three years of the study and along the 

cables. EMF strength dissipated relatively quickly with distance from the cable and approached background 

levels at about one meter from the cable. The EMF at unenergized cables was similar to that found at the 

natural habitats.

4) The potential effectiveness of the commonly proposed mitigation of cable burial.

Given the rapidity with which the EMF produced by the energized cables diminishes and the lack of response 

to that EMF by the fishes and invertebrates in this study, cable burial would not appear necessary strictly for 

biological reasons. In this and similar cases, cable burial, at sufficient depth, would be an adequate tool to 

prevent EMF emissions from being present at the seafloor.

Acknowledgment

We thank Linda Snook for identifying the fishes and invertebrates from the videotapes. This research was 

conducted aboard the RV Velero and we thank Captain Irv Leask and all of its crew for their help. The 

DeepWorker and Dual DeepWorker were built and operated by Nuytco and we thank head pilot Jeff Heaton 

and all of the pilots and crew of these submersibles for the great work. We also thank Donna Schroeder for 

her able assistance aboard the Dual DeepWorker.

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57

Figure 3-1. Location of the offshore energized and unenergized submarine power cables surveyed in this study.

HONDO

Offshore

76–213 m

HARMONY

HERITAGE

(A)

(B)

(C)

(C1

)

Pipe

C A L I F O R N I A

Area

Detailed
58

Figure 3-2. A photograph of the method used to assess the electromagnetic fields occurring around energized and 

unenergized submarine power cables and natural habitats. 
59

Figure 3-3. Locations of transects conducted over energized and unenergized cables and natural habitats, 2012. During 

this year cables A and B were energized and cables C and C1 were unenergized.

81m

85m

147m

125m

100m

150m

175m

200m

A B C1

C

0 1,000 Meters

2012 Cable survey

depth category

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17
60

Figure 3-4. Locations of transects conducted over energized and unenergized cables and natural habitats, 2013. 

During this year cable A was energized, cables B and C were unenergized and C1 were neither surveyed nor was the 

electromagnetic field measured. 

81m

85m

147m

125m

100m

150m

175m

200m

A B C1

C

0 1,000 Meters

2013 Cable survey

depth category

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17
61

Figure 3-5. Locations of transects conducted over energized and unenergized cables and natural habitats, 2014. During 

this year cables A and B were energized and cables C and C1 were unenergized.

81m

85m

147m

125m

100m

150m

175m

200m

A B C1

C

0 1,000 Meters

2014 Cable survey

depth category

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17
62

Figure 3-6. A 2-d multiple dimensional scaling model comparing the fish assemblages observed over energized and 

unenergized cables and natural habitats surveyed during 2012–2014. Numbers near symbols refer to the depth category 

of that transect. The higher the number the deeper the transect. Depth ranges of the depth categories are given in Table 

3-1.

Fish Assemblage by Habitat Type

Energized Cable A

Energized Cable B

Energized Cable C1

Unenergized Cable B

Unenergized Cable C

Natural Habitat

Similarity

35

45
63

Figure 3-7. Densities of all fishes between all cables (energized and unenergized) combined and natural habitats of 

major species or species groups. Densities are in fishes per 100 m3 and means and standard deviations are provided. 

0

10

20

30

40

50

Density

Cables Natural Habitats 

Total Fish Densities
64

Figure 3-8. Densities of important fish species (defined as comprising at least 1% of all fishes observed), comparing 

1) energized and unenergized cables and 2) natural habitats. Densities are in fish per 100 m3 and means and standard 

deviations are provided. 

0.0

0.2

0.4

0.6

0.8

1.0

0

10

20

30

40

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0.0

0.2

0.4

0.6

0.8

1.0

0

1

2

3

4

5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.0

0.2

0.4

0.6

0.8

0

1

2

3

4

Density

Halfbanded Rockfish Stripetail Rockfish

Unidentified Poachers

Unidentified Eelpouts Shortspine Combfish Greenstriped Rockfish

Lingcod

Unidentified Sanddabs

Cables Natural Habitats

Cables Natural Habitats

Cables Natural Habitats Cables Natural Habitats

Cables Natural Habitats

Cables Natural Habitats Cables Natural Habitats

Cables Natural Habitats

NS NS
65

Figure 3-9. Length frequencies of all fishes observed on energized and unenergized cables and natural habitats, 

2012–2014.

0.00

0.10

0.20

0.30

0.40

0.50

0 10 20 30 40 50 60 70 80 90 100 110

0.00

0.10

0.20

0.30

0.40

0.50

0 10 20 30 40 50 60 70 80 90 100 110

0.00

0.10

0.20

0.30

0.40

0.50

0 5 10 20 30 40 50 60 70 80 90 100 110

Proportion Proportion Proportion

Total Length (cm)

Total Length (cm)

Total Length (cm)

Length Frequencies of All Fishes Observed

Energized Cables N=4,452

Unenergized Cables N=3,681

Natural Habitats N=1,522

X=13.7 cm

X=14.8 cm

X=13.0 cm
66

Figure 3-10. A 2-d multiple dimensional scaling model comparing the invertebrate assemblages observed over 

energized and unenergized cables and natural habitats surveyed during 2012–2014. Numbers near symbols refer to the 

depth category of that transect. The higher the number the deeper the transect. Depth ranges of the depth categories 

are given in Table 3-1.

Invertebrate Assemblage by Habitat Type

Energized Cable A

Energized Cable B

Energized Cable C1

Unenergized Cable B

Unenergized Cable C

Natural Habitat

Similarity

55

68
67

Figure 3-11. Densities of important invertebrate species (defined as comprising at least 1% of all invertebrates observed) 

between all cables (energized and unenergized) combined and natural habitats of major species or species groups. 

Densities are in invertebrates per 100 m3 and means and standard deviations are provided

0

10

20

30

40

50

60

0

10

20

30

0

1

2

3

4

5

6

0

2

4

6

8

0

5

10

15

20

25

30

0

1

2

3

4

5

6

0

2

4

6

8

Density

Density

Density

Density

Density

Density

Density

White-Plumed Anemone

California Sea Cucumber

Red Octopus White Sea Urchin

Sand Star

Spot Prawn Sea Pens Thin

Cables Natural Habitats Cables Natural Habitats Cables Natural Habitats

Cables Natural Habitats Cables Natural Habitats

Cables Natural Habitats Cables Natural Habitats

0.0

0.5

1.0

1.5

2.0

2.5

Density

Unidentified Urticina Anemone

Cables Natural Habitats

0.0

0.5

1.0

1.5

2.0

2.5

Density

Black Crinoid

Cables Natural Habitats
68

2012 Cable A B C C1 Natural Habitat

Energized Energized Unenergized Not Surveyed

Transect 

Category

Depth Range

(m)

9 104–128 156 164 229

10 112–144 97 181 206

11 137–153 168 163 146 237

12 146–154 170 182 183 188

13 162–180 285 197 234

14 175–192 240 267 195

f 187–204 208

2013 Cable A B C C1 Natural Habitat

Energized Unenergized Unenergized Not Surveyed

West East West East West East

Transect 

Category

Depth Range

(m)

1 76–79 214 160 159

2 80–81 179 238 167

3 81–82 237 268 344

4 82–84 208 186 180

5 83–87 251 200 272

6 86–87 135

7 90–95

8 94–107

9 104–128 142 158 136 225 178 89

10 112–144 69 163 104 99 185

11 137–153 88 91 137 121 175

12 146–154 169 182 202

13 162–180

14 175–192

15 187–204 174 222 190

16 192–203 105 162 82 177

17 200–213 241

Table 3-1. Locations and lengths of transects made at energized and unenergized cables and natural habitat in 2012–

2014. Transects are divided into depth categories and lengths are in meters. See Figures 3-3, 3-4, and 3-5 for locations.
69

2014 Cable A B C C1 Natural Habitat

Energized Energized Unenergized Unenergized

West East West East West East

Transect 

Category

Depth Range

(m)

7 90–95 143 100

8 94–107 124 100 60

9 104–128 59 61 93 90 110

10 112–141 143 139 107 96 161

11 137–153 98 112 137 122 122 129 133

Table 3-1. Continued. Locations and links of transects made at energized and unenergized cables and natural habitat 

in 2012–2014. Transects are divided into depth categories and lengths are in meters. See Figures 3-3, 3-4, and 3-5 for 

locations.
70

EMF (μT)

Location Bottom Depth (m) Distance from Cable

0 m 0.5 m 1 m

1 108 67.6 22.6 3.2

2 112 107.7 26.5 20.1

3 135 91.1 39.8 4.1

4 158 106.0 31.3 2.7

Mean 93.1 30.1 7.5

SD 18.6 7.4 8.4

Table 3-2. Electromagnetic fields (EMFs) in microteslas (μT) measured at Cable A in 2012. Measurements were taken 

at three distances from the cable (0 m – on cable, 0.5 m, and 1 m) and at four locations along cable.
71

2012

Site N Mean EMF SD Min. Max.

A (energized) 6 101.2 19.2 67.6 120.7

B (energized) 3 110.1 10.3 101.5 121.5

C (unenergized) 4 1.2 0.3 0.9 1.5

C1 (unenergized) 1 1.2

Natural Habitat 4 0.9 0.1 0.8 1

2013

A (energized) 4 85.3 30.7 51 115

B (unenergized) 3 0.4 0.1 0.3 0.5

C (unenergized) 1 0.3

C1 (unmeasured)

Natural Habitat 1 0.3

2014

A (energized) 3 100.7 45.4 51 140

B (energized) 1 36.2

C (unenergized) 5 0.0 0.0 0 0

C1 (energized) 2 178.0 38.2 151 205

Natural Habitat 1 0.3

Table 3-3. Mean, minimum, and maximum electromagnetic fields (EMFs) in microteslas (μT) (with standard 

deviations) measured directly on cables A, B, C, and C1, and on the natural habitat during 2012, 2013, and 2014. N = 

the number of sites along a cable where EMF was measured during the surveys.
72

Table 3-4. Effects of cable state (energized, unenergized), side of cable surveyed (west, east) nested in cable state, 

stratum group (1–4), and year (2012–2014) on fish density tested using a generalized linear model (normal distribution, 

identity link), p<0.05. Densities were log(x+1) transformed. Cable State = energized or unenergized. Stratum groups 

are discussed under Results. * = statistically significant.

Taxon Whole Model 

Difference Cable State Cable Side Stratum Groups Year

DF 8 1 2 3 2

Halfbanded rockfish X2 26.133 1.116 0.210 6.707 13.735

p 0.0010* 0.2908 0.9003 0.0819 0.0010*

Stripetail rockfish X2 54.474 3.344 0.549 51.093 9.687

p <.0001* 0.0674 0.7599 <.0001* 0.0079*

Unidentified poachers X2 57.808 2.761 0.142 49.148 6.836

p <.0001* 0.0966 0.9314 <.0001* 0.0328

Shortspine combfish X2 46.427 0.793 10.287 22.828 5.225

p <.0001* 0.3731 0.0058* <.0001* 0.0733

Greenstriped rockfish X2 36.740 3.583 1.320 18.111 5.222

p <.0001* 0.0584 0.5168 0.0004* 0.0735

Lingcod X2 25.439 2.178 0.867 10.116 20.052

p 0.0013* 0.1400 0.6484 0.0176* <.0001*

Unidentified sanddabs X2 12.909 0.331 0.993 7.405 4.965

p 0.1150 0.5649 0.6088 0.0601 0.0835

Unidentified eelpouts X2 51.044 0.103 0.191 45.158 2.645

p <.0001* 0.7484 0.9091 <.0001* 0.2665

Total fishes X2 8.7853 2.1205 1.0314 1.4355 3.2553

p 0.3607 0.1453 0.5971 0.6972 0.1964
73

Welch’s Test

Energized Cable v Unenergized Cable

F Ratio df p

260.36 1 <.0001

Energized Cable v Natural Habitats

F Ratio df p

18.37 1 <.0001

Unenergized Cable v Natural Habitats

F Ratio df p

36.51 1 <.0001

Kolmogorov Smirnov Two-Sample Test

Energized Cable v Unenergized Cable

N KS p

8,146 0.142 <.0001

Energized Cable v Natural Habitats

N KS p

5,984 0.060 <.0001

Unenergized Cable v Natural Habitats

N KS p

5,220 0.067 <.0001

Table 3-5. Comparisons of the mean sizes and size frequency distributions of fishes observed over energized and 

unenergized cables and natural habitats in southern California, 2012–2014. Mean sizes were compared with the Welch’s 

Test and size frequency distributions using the Kolmogorov Smirnov Two-Sample Test.
74

Bearded eelpout Lyconema barbatum

Bigfin eelpout Lycodes cortezianus

Blackbelly eelpout Lycodes pacificus

Bluebarred prickleback Plectobranchus evides

Bocaccio Sebastes paucispinis

Bull sculpin Enophrys taurina

Calico rockfish Sebastes dallii

California lizardfish Synodus lucioceps

California skate Raja inornatus

California smoothtongue Leuroglossus stilbius

Copper rockfish Sebastes caurinus

Cowcod Sebastes levis

Darkblotched rockfish Sebastes crameri

Dover sole Microstomus pacificus

English sole Parophrys vetulus

Flag rockfish Sebastes rubrivinctus

Greenblotched rockfish Sebastes rosenblatti

Greenspotted rockfish Sebastes chlorostictus

Greenstriped rockfish Sebastes elongatus

Halfbanded rockfish Sebastes semicinctus

Icelinus sculpins Icelinus spp.

Lingcod Ophiodon elongatus

Longspine combfish Zaniolepis latipinnis

Pacific argentine Argentina sialis

Pacific hake Merluccius productus

Pacific sanddab Citharichthys pacificus

Pink surfperch Zalembius rosaceus

Pygmy rockfish Sebastes wilsoni

Shortspine combfish Zaniolepis frenata

Speckled sculpin Citharichthys stigmaeus

Spotted ratfish Hydrolagus colliei

Splitnose rockfish Sebastes diploproa

Spotfin sculpin Icelinus tenuis

Stripetail rockfish Sebastes saxicola

Swordspine rockfish Sebastes ensifer

Threadfin sculpin Icelinus filamentosus

Treefish Sebastes serriceps

Unidentified eelpout Zoarcidae

Unidentified fishes Osteichthyes

Unidentified flatfishes Pleuronectiformes

Unidentified combfishes Zaniolepis spp.

Unidentified cuskeel Ophidiidae

Unidentified poachers Agonidae

Unidentified rockfishes Sebastes spp.

Unidentified pricklebacks Stichaeidae

Unidentified sanddabs Citharichthys spp.

Unidentified sculpins Cottidae

Unidentified Sebastomus Sebastomus spp.

Vermilion rockfish Sebastes miniatus

Wolf-eel Anarrhichthys ocellatus

Table 3-6. Common and scientific names of fishes observed at bottom depths of 76–213 m over energized and 

unenergized cables and natural habitats in southern California, 2012–2014.
75

Table 3-7. All fishes observed at bottom depths of 76–213 m near and over energized and unenergized cables and on natural 

habitats in southern California, 2012–2014. Density is in fish per 100 m3. FO = frequency of occurrence (of 85 transects).

Common Name Number Density Percent Abundance FO

Halfbanded rockfish 4,154 9.1 42.9 59

Unidentified flatfishes 1,449 2.3 15.0 81

Stripetail rockfish 702 1.4 7.3 31

Unidentified poachers 596 1.2 6.2 75

Unidentified fishes 333 0.6 3.4 77

Shortspine combfish 312 0.6 3.2 61

Unidentified combfishes 284 0.6 2.9 71

Unidentified rockfishes 294 0.5 3.0 60

Greenstriped rockfish 208 0.4 2.1 53

Lingcod 182 0.4 1.9 59

Unidentified sanddabs 170 0.3 1.8 55

Unidentified eelpouts 183 0.3 1.9 34

Unidentified Sebastomus rockfishes 98 0.2 0.9 37

Longspine combfish 91 0.2 0.9 28

Greenspotted rockfish 61 0.1 0.6 21

Pacific argentine 53 0.1 0.5 19

Flag rockfish 38 0.1 0.4 17

Unidentified sculpins 61 0.1 0.6 21

California lizardfish 45 0.1 0.5 20

Pacific hake 53 0.1 0.5 7

Pink surfperch 45 0.1 0.5 21

Bigfin eelpout 39 0.1 0.4 18

Pygmy rockfish 26 0.1 0.3 2

Greenblotched rockfish 20 0.1 0.2 11

Bocaccio 27 <0.1 0.3 11

English sole 18 <0.1 0.2 14

Calico rockfish 19 <0.1 0.2 7

Cowcod 13 <0.1 0.1 11

Spotfin sculpin 11 <0.1 0.1 4

Vermilion rockfish 8 <0.1 <0.1 2

Copper rockfish 13 <0.1 0.1 3

Splitnose rockfish 10 <0.1 0.1 4

Unidentified pricklebacks 9 <0.1 <0.1 6

Swordspine rockfish 7 <0.1 <0.1 5

Blackbelly eelpout 8 <0.1 <0.1 3

Spotted ratfish 5 <0.1 <0.1 4

Wolf-eel 4 <0.1 <0.1 4

Pacific sanddab 4 <0.1 <0.1 3

Darkblotched rockfish 4 <0.1 <0.1 2

Bluebarred prickleback 3 <0.1 <0.1 2

Bearded eelpout 2 <0.1 <0.1 2

Treefish 2 <0.1 <0.1 2

Speckled sanddab 1 <0.1 <0.1 1

Bull sculpin 1 <0.1 <0.1 1

Threadfin sculpin 1 <0.1 <0.1 1

Icelinus sculpin 1 <0.1 <0.1 1

California smoothtongue 1 <0.1 <0.1 1

Unidentified cuskeel 1 <0.1 <0.1 1

California skate 1 <0.1 <0.1 1

Totals 9,675 19.15 85
76

Common Name Number Density Percent 

Abundance FO

Halfbanded rockfish 2494 14.5 56.0 28

Unidentified flatfishes 430 1.8 9.7 30

Unidentified poachers 194 1.1 4.4 29

Stripetail rockfish 211 0.9 4.7 11

Shortspine combfish 147 0.7 3.3 28

Unidentified combfishes 136 0.7 3.1 30

Unidentified fishes 130 0.6 2.9 30

Unidentified rockfishes 118 0.5 2.6 25

Lingcod 96 0.5 2.2 30

Greenstriped rockfish 84 0.4 1.9 23

Unidentified sanddabs 74 0.3 1.7 19

Unidentified Sebastomus rockfishes 42 0.2 0.9 17

Longspine combfish 47 0.2 1.1 11

Flag rockfish 26 0.2 0.6 9

Pygmy rockfish 26 0.1 0.6 2

Pink seaperch 24 0.1 0.5 10

Greenspotted rockfish 19 0.1 0.4 8

Pacific argentine 15 0.1 0.3 7

Unidentified sculpins 25 0.1 0.6 9

Unidentified eelpouts 20 0.1 0.4 10

California lizardfish 16 0.1 0.4 6

Greenblotched rockfish 10 0.1 0.2 5

Spotfin sculpin 9 <0.1 0.2 3

Pacific hake 5 <0.1 0.1 2

Unidentified pricklebacks 7 <0.1 0.2 4

Cowcod 5 <0.1 0.1 5

Calico rockfish 7 <0.1 0.2 4

Swordspine rockfish 4 <0.1 0.1 3

English sole 5 <0.1 0.1 4

Bigfin eelpout 6 <0.1 0.1 3

Wolf-eel 3 <0.1 0.1 3

Spotted ratfish 3 <0.1 0.1 3

Bocaccio 3 <0.1 0.1 2

Bluebarred prickleback 3 <0.1 0.1 2

Dover sole 3 <0.1 0.1 2

Splitnose rockfish 2 <0.1 <0.1 2

Unidentified cuskeels 1 <0.1 <0.1 1

California smoothtongue 1 <0.1 <0.1 1

Icelinus sculpin 1 <0.1 <0.1 1

Treefish 1 <0.1 <0.1 1

Bull sculpin 1 <0.1 <0.1 1

Pacific sanddab 1 <0.1 <0.1 1

Totals 4,455 23.8 100.0 34

Table 3-8. All fishes observed at bottom depths of 76–203 m over and near energized cables in southern California, 

2012–2014. Density is in fish per 100 m3

. FO = frequency of occurrence (of 34 transects).
77

Common Name Number Density Percent 

Abundance FO

Halfbanded rockfish 1,382 8.4 37.4 21

Stripetail rockfish 470 2.9 12.7 13

Unidentified flatfishes 459 2.2 12.4 29

Unidentified poachers 307 1.8 8.3 29

Unidentified rockfishes 149 0.9 4.0 22

Shortspine combfish 122 0.6 3.3 21

Unidentified fishes 110 0.6 3.0 27

Greenstriped rockfish 100 0.6 2.7 23

Unidentified combfishes 98 0.6 2.7 25

Lingcod 67 0.4 1.8 20

Unidentified sanddabs 49 0.3 1.3 19

Unidentified Sebastomus rockfishes 43 0.3 1.2 16

Greenspotted rockfish 37 0.2 1.0 10

Pacific hake 44 0.2 1.2 3

Pacific argentine 30 0.2 0.8 8

Longspine combfish 28 0.1 0.8 10

Bocaccio 22 0.1 0.6 8

Pink seaperch 17 0.1 0.5 8

Flag rockfish 11 0.1 0.3 7

Unidentified sculpins 20 0.1 0.5 6

Unidentified eelpouts 17 0.1 0.5 9

English sole 11 0.1 0.3 8

California lizardfish 11 0.1 0.3 7

Vermilion rockfish 8 0.1 0.2 2

Copper rockfish 13 0.1 0.4 3

Calico rockfish 12 0.1 0.3 3

Bigfin eelpout 9 <0.1 0.2 7

Cowcod 7 <0.1 0.2 5

Greenblotched rockfish 7 <0.1 0.2 4

Splitnose rockfish 8 <0.1 0.2 2

Blackbelly eelpout 5 <0.1 0.1 1

Spotted ratfish 2 <0.1 0.1 1

Swordspine rockfish 3 <0.1 0.1 2

Unidentified pricklebacks 2 <0.1 0.1 2

Darkblotched rockfish 3 <0.1 0.1 1

Dover sole 1 <0.1 <0.1 1

Threadfin sculpin 1 <0.1 <0.1 1

Treefish 1 <0.1 <0.1 1

Wolf-eel 1 <0.1 <0.1 1

Bearded eelpout 1 <0.1 <0.1 1

California skate 1 <0.1 <0.1 1

Pacific sanddab 1 <0.1 <0.1 1

Speckled sanddab 1 <0.1 <0.1 1

Totals 3,691 21.2 100.0% 29

Table 3-9. All fishes observed at bottom depths of 104–213 m over and near unenergized cables in southern California, 

2012–2014. Density is in fish per 100 m3

. FO = frequency of occurrence (of 29 transects).
78

Common Name Number Density Percent 

Abundance FO

Unidentified flatfishes 560 3.2 36.6 22

Halfbanded rockfish 278 1.7 18.2 10

Unidentified eelpouts 146 0.9 9.5 15

Unidentified poachers 95 0.7 6.2 17

Unidentified fishes 93 0.6 6.1 20

Unidentified combfishes 50 0.4 3.3 16

Unidentified sanddabs 47 0.3 3.1 17

Shortspine combfish 43 0.3 2.8 12

Unidentified rockfishes 27 0.2 1.8 13

Greenstriped rockfish 24 0.2 1.6 7

Bigfin eelpout 24 0.1 1.6 8

Stripetail rockfish 21 0.1 1.4 7

California lizardfish 18 0.1 1.2 7

Lingcod 19 0.1 1.2 9

Longspine combfish 16 0.1 1.0 7

Unidentified sculpins 16 0.1 1.0 6

Unidentified Sebastomus rockfishes 13 0.1 0.9 4

Pacific argentine 8 0.1 0.5 4

Greenspotted rockfish 5 <0.1 0.3 3

Pink seaperch 4 <0.1 0.3 3

Pacific hake 4 <0.1 0.3 2

Blackbelly eelpout 3 <0.1 0.2 2

Greenblotched rockfish 3 <0.1 0.2 2

English sole 2 <0.1 0.1 2

Bocaccio 2 <0.1 0.1 1

Pacific sanddab 2 <0.1 0.1 1

Spotfin sculpin 2 <0.1 0.1 1

Bearded eelpout 1 <0.1 0.1 1

Cowcod 1 <0.1 0.1 1

Darkblotched rockfish 1 <0.1 0.1 1

Flag rockfish 1 <0.1 0.1 1

Totals 1,529 9.4 100.0 22

Table 3-10. All fishes observed at bottom depths of 76–204 m over natural habitats in southern California, 2012–2014. 

Density is in fish per 100 m3. FO = frequency of occurrence (of 22 transects).
79

Table 3-11. Effects of cable state (energized, unenergized), side of cable surveyed (W, E) nested in cable state, stratum 

group (1-4), and year (2012-2014) on invertebrate density tested using a generalized linear model (normal distribution, 

identity link), p<0.05. Densities were log(x+1) transformed. Cable State = energized or unenergized. Stratum groups 

are discussed under Results. * = statistically significant.

Taxon Whole Model 

Difference Cable State Cable Side Stratum Groups Year

DF 8 1 2 3 2

White-plumed anemone X2 77.190 5.485 1.564 57.817 7.843

p <.0001* 0.019 0.458 <.0001* 0.020*

Spot prawn X2 73.407 0.911 0.271 56.182 37.781

p <.0001* 0.340 0.873 <.0001* <.0001*

Sea pen, thin X2 93.957 0.009 66.213 46.116 9.299

p <.0001* 0.925 <.0001* <.0001* 0.010*

California sea cucumber X2 80.209 1.141 2.368 75.479 5.471

p <.0001* 0.285 0.306 <.0001* 0.065

Sand star X2 45.971 12.983 0.960 4.591 24.452

p <.0001* 0.0003* 0.619 0.204 <.0001*

Red octopus X2 27.199 0.019 14.847 10.446 0.003

p 0.001* 0.889 0.001* 0.015* 0.999

Unidentified Urticina

anemone X2 75.522 5.480 1.954 58.734 4.900

<.0001* 0.019 0.376 <.0001* 0.086

Black crinoid X2 42.274 7.728 6.192 27.052 12.625

p <.0001* 0.005* 0.045 <.0001* 0.002*

White sea urchin X2 11.896 1.430 7.024 2.203 3.951

p 0.156 0.232 0.030* 0.531 0.139

Total invertebrates X2 53.719 5.147 2.146 48.160 11.601

p <.0001* 0.023* 0.342 <.0001* 0.003*
80

Acanthogorgia gold corals Acanthogorgia spp.

Basket star Gorgonocephalus eucnemis

Bat star Asterina miniata

Bat star/red sea star Asterina miniata/M. aequalis

Brittle star Ophiopsila californica

Brown box crab Lopholithodes foraminatus

Buccinidae whelks Buccinidae

California sea cucumber Apostichopus californicus

Cancer crabs Cancer spp.

Ceremaster cookie star Ceramaster spp.

Christmas tree coral Antipathes dendrochristos

Fish-eating anemone Urticina piscivora

Fragile pink urchin Strongylocentrotus fragilis

Henricia blood stars Henricia sp.

King crab Paralithodes californiensis

Leptasterias six-arm sea star Leptasterias spp.

Linckia sea stars Linckia spp.

Orthasterias rainbow stars Orthasterias spp.

Painted urticina Urticina crassicornis

Paragorgia sea fan (white with red polyps) Paragorgia spp.

Parastichopus sea cucumbers Parastichopus spp.

Psolus slipper sea cucumber Psolus spp.

Ptilosarcus orange sea pens Ptilosarcus sp.

Red gorgonian Leptogorgia chilensis

Red octopus Octopus rubescens

Red sea star Mediaster aequalis

Sand Star Luidia spp.

Sea pens thick Pennatulacea 

Sea pens thin Pennatulacea

Sea slug Pleurobranchaea californica

Serpula worms Serpula sp.

Solaster sea stars Solaster sp.

Spot prawn Pandalus platyceros

Stylasterias fish-eating sea stars Stylasterias spp.

Unidentified anemones Actinaria

Unidentified brachiopods Brachiopoda

Unidentified crabs Malacostraca

Unidentified black crinoid Crinoidea

Unidentified corals Hexacorallia/Octocorallia

Unidentified gastropods Gastropoda

Unidentified gorgonians Holaxonia

Unidentified hydroids Hydrozoa

Unidentified invertebrates Invertebrata

Unidentified nudibranchs Opistobranchia

Unidentified red sea fans Swiftia spp.

Unidentified sea pen (thin) Pennatulacea 

Unidentified sea stars Asteroidea

Unidentified sea urchins Echinoidea

Unidentified sponges Porifera

Unidentified tunicates Aplidium sp.

Unidentified sunstars Pycnopodia/Rathbunaster

Urticina anemones Urticina spp.

Tube-dwelling anemones Cerianthidae

White-plumed anemone Metridium farcimen

White sea urchin Lytechinus pictus

Table 3-12. Common and scientific names of invertebrates observed at bottom depths of 76–213 m over energized and 

unenergized cables and natural habitats in southern California, 2012–2014.
81

Common Name Number Density Percent Abundance FO

White-plumed anemone 13,232 28.4 43.4 74

Spot prawn 4,407 9.8 14.4 21

Sea pen thin 5,582 9.4 18.3 82

California sea cucumber 1,610 3.1 5.3 73

Sand star 1,617 2.9 5.3 83

Red octopus 1,215 2.1 4.0 83

Unidentified Urticina anemone 388 0.8 1.3 50

Black crinoid 371 0.8 1.3 42

White sea urchin 451 0.6 1.5 11

Sea slug 243 0.5 0.8 69

Serpulid worms 173 0.4 0.6 23

Fragile pink urchin 176 0.4 0.6 11

Unidentified invertebrates 105 0.2 0.3 42

Tube dwelling anemones 128 0.2 0.3 36

Unidentified gorgonians 107 0.2 0.3 18

Fish-eating star 80 0.2 0.3 32

Cancer crab 80 0.1 0.3 37

Sea pen thick 77 0.1 0.3 21

Unidentified whelks 56 0.1 0.2 19

Unidentified sea stars 58 0.1 0.2 32

Bat star 65 0.1 0.2 19

Red sea fans 36 0.1 0.1 13

Painted Urticina 34 0.1 0.1 15

Unidentified corals 43 0.1 0.1 17

Fish-eating anemone 33 0.1 0.1 13

Brachiopoda 9 <0.1 <0.1 1

Unidentified anemones 19 <0.1 0.1 9

Sunstar 19 <0.1 0.1 13

Red sea star 18 <0.1 0.1 11

Slipper sea cucumber 8 <0.1 <0.1 4

Unidentified crabs 11 <0.1 <0.1 7

Basket star 9 <0.1 <0.1 5

Unidentified sea fans 6 <0.1 <0.1 2

Unidentified gastropods 10 <0.1 <0.1 2

Unidentified sponges 8 <0.1 <0.1 3

Unidentified hydroids 5 <0.1 <0.1 3

Blood star 4 <0.1 <0.1 4

Cookie star 2 <0.1 <0.1 2

King crab 3 <0.1 <0.1 3

Red gorgonians 3 <0.1 <0.1 3

Rainbow star 2 <0.1 <0.1 2

Brown box crab 2 <0.1 <0.1 1

Gold coral 1 <0.1 <0.1 1

Six-arm sea star 1 <0.1 <0.1 1

Christmas tree coral 2 <0.1 <0.1 2

Orange sea pen 2 <0.1 <0.1 2

Sea star 2 <0.1 <0.1 2

Unidentified sea urchins 2 <0.1 <0.1 1

Bat star/red sea star 2 <0.1 <0.1 2

Brittle star 1 <0.1 <0.1 1

Sun star 1 <0.1 <0.1 1

Unidentified nudibranch 1 <0.1 <0.1 1

Sea fan (white with red polyps) 1 <0.1 <0.1 1

Tunicate 1 <0.1 <0.1 1

Unidentified sea cucumber 1 <0.1 <0.1 1

Total Invertebrates 30,523 61.0 100 85

Table 3-13. All invertebrates observed at bottom depths of 76–213 m over or near energized and unenergized cables 

and natural habitats in southern California, 2012–2014. Density is in invertebrates per 100 m3. FO = frequency of 

occurrence (of 85 transects).
82

Common Name Number Density Percent 

Abundance FO

White-plumed anemone 5,347 29.8 39.9 34

Sea pen thin 3,311 13.5 24.7 31

Spot prawn 2,023 13.3 15.1 8

California sea cucumber 638 3.3 4.8 31

Sand star 569 2.7 4.3 33

Red octopus 379 1.7 2.8 33

Black crinoid 285 1.7 2.1 22

Unidentified urticina anemones 172 1.0 1.3 26

Sea slug 98 0.5 0.7 27

Serpulid worms 55 0.3 0.4 13

Unidentified invertebrates 47 0.3 0.4 16

Tube dwelling anemone 57 0.2 0.4 16

Unidentified gorgonians 51 0.2 0.4 9

Fish-eating star 38 0.2 0.3 18

Sea pen thick 41 0.2 0.3 11

Unidentified corals 29 0.2 0.2 10

Cancer crab 32 0.2 0.2 16

Red sea fan 20 0.2 0.1 6

Fragile pink urchin 20 0.1 0.1 3

Unidentified whelks 24 0.1 0.1 11

Painted urticina 18 0.1 0.1 7

Fish-eating anemone 18 0.1 0.1 5

Brachiopoda 9 0.1 0.1 1

Unidentified sea stars 17 0.1 0.1 13

Unidentified anemones 17 0.1 0.1 8

Bat star 12 0.1 0.1 9

Slipper sea cucumber 7 0.1 0.1 3

Unidentified crabs 7 <0.1 0.1 5

Unidentified gastropods 10 <0.1 0.1 2

Basket star 7 <0.1 0.1 4

Red sea star 7 <0.1 0.1 3

Unidentified sponges 6 <0.1 <0.1 1

Sunstar 4 <0.1 <0.1 4

White sea urchin 2 <0.1 <0.1 2

Brown box crab 2 <0.1 <0.1 1

Red gorgonian 2 <0.1 <0.1 2

King crab 1 <0.1 <0.1 1

Blood star 1 <0.1 <0.1 1

Sun star 1 <0.1 <0.1 1

Unidentified nudibranch 1 <0.1 <0.1 1

Paragorgia sea fan 1 <0.1 <0.1 1

Unidentified hydroid 1 <0.1 <0.1 1

Sea star 1 <0.1 <0.1 1

Totals 13,388 70.0 100 34

Table 3-14. All invertebrates observed at bottom depths of 76–203 m over or near energized cables in southern 

California, 2012–2014. Density is in invertebrates per 100 m3. FO = frequency of occurrence (of 34 transects).
83

Common Name Number Density Percent 

Abundance FO

White-plumed anemone 7,671 47.3 52.5 29

Spot prawn 2,360 13.3 16.1 9

Sea pen thin 1,548 8.0 10.6 29

California sea cucumber 892 4.8 6.1 27

Sand star 790 4.1 5.4 29

Red octopus 339 1.8 2.3 28

Unidentified urticina anemones 213 1.4 1.5 21

Serpulid worms 115 0.8 0.7 8

Sea slug 97 0.6 0.7 26

Fragile pink urchin 83 0.5 0.6 5

Black crinoid 55 0.3 0.3 14

Unidentified gorgonians 56 0.3 0.3 9

Fish-eating star 42 0.2 0.3 14

Unidentified invertebrates 40 0.2 0.3 16

Cancer crab 40 0.2 0.3 17

Bat star 47 0.2 0.3 8

Unidentified sea stars 30 0.2 0.2 12

Tube dwelling anemone 34 0.1 0.2 10

Unidentified whelks 29 0.1 0.2 6

Painted urticina 15 0.1 0.1 7

Sea pen thick 14 0.1 0.1 6

Red sea fan 13 0.1 0.1 6

Sunstar 14 0.1 0.1 8

Fish-eating anemone 13 0.1 0.1 6

Unidentified corals 11 0.1 0.1 6

Unidentified sea fans 6 0.1 <0.1 2

Red sea star 9 0.1 0.1 6

White sea urchin 13 0.1 0.1 3

Unidentified hydroids 4 <0.1 <0.1 2

Unidentified crabs 4 <0.1 <0.1 2

Cookie star 2 <0.1 <0.1 2

Blood star 2 <0.1 <0.1 2

Unidentified anemones 2 <0.1 <0.1 1

Unidentified sponges 2 <0.1 <0.1 2

Rainbow star 2 <0.1 <0.1 2

Gold coral 1 <0.1 <0.1 1

Six-arm sea star 1 <0.1 <0.1 1

Unidentified sea urchins 2 <0.1 <0.1 1

Brittle star 1 <0.1 <0.1 1

Slipper sea cucumber 1 <0.1 <0.1 1

Red gorgonian 1 <0.1 <0.1 1

Tunicate 1 <0.1 <0.1 1

Christmas tree coral 1 <0.1 <0.1 1

Unidentified sea star 1 <0.1 <0.1 1

King crab 1 <0.1 <0.1 1

Bat star/red sea star 1 <0.1 <0.1 1

Totals 14,619 84.9 100 29

Table 3-15. All invertebrates observed at bottom depths of 104–213 m over or near unenergized cables in southern 

California, 2012–2014. Density is in invertebrates per 100 m3

. FO = frequency of occurrence (of 29 transects).
84

Common Name Number Density Percent 

Abundance FO

Sea pen thin 723 4.9 28.7 22

Red octopus 497 3.2 19.6 22

White sea urchin 436 2.2 17.3 6

Sand star 258 1.5 10.3 21

White-plumed anemone 214 1.4 8.5 11

Fragile pink urchin 73 0.5 2.9 3

California sea cucumber 80 0.5 3.2 15

Sea slug 48 0.3 1.9 16

Black crinoid 31 0.2 1.2 6

Tube dwelling anemone 37 0.2 1.5 10

Spot prawn 24 0.2 0.9 4

Sea pen thick 22 0.1 0.9 4

Unidentified invertebrates 18 0.1 0.7 10

Unidentified sea stars 11 0.1 0.4 7

Cancer crab 8 0.1 0.3 4

Unidentified whelks 3 <0.1 0.1 2

Bat star 6 <0.1 0.2 2

Unidentified urticina anemone 3 <0.1 0.1 3

Serpulid worms 3 <0.1 0.1 2

Unidentified corals 3 <0.1 0.1 1

Red sea fan 3 <0.1 0.1 1

Basket star 2 <0.1 <0.1 1

Fish-eating anemone 2 <0.1 <0.1 2

Orange sea pen 2 <0.1 <0.1 2

Red sea star 2 <0.1 <0.1 2

Painted urticina 1 <0.1 <0.1 1

King crab 1 <0.1 <0.1 1

Blood star 1 <0.1 <0.1 1

Christmas tree coral 1 <0.1 <0.1 1

Sunstar 1 <0.1 <0.1 1

Sea cucumber 1 <0.1 <0.1 1

Bat star/red sea star 1 <0.1 <0.1 1

Totals 2,516 15.4 100 22

Table 3-16. All invertebrates observed at bottom depths of 76–204 m over natural habitats in southern California, 

2012–2014. Density is in invertebrates per 100 m3

. FO = frequency of occurrence (of 22 transects).
85

Red Octopus

Number Mean Density SD

Side

West 21 0.95 0.62083

East 42 2.16 1.43992

Model DF X2 p

Side Surveyed 1 14.460 0.0001

Sea Pen Thin

Number Mean Density SD

Side

West 21 1.78 3.0911

East 42 15.56 13.5315

Model DF X2 p

Side Surveyed 1 42.284 <.0001

Table 3-17. Effect of cable side (energized and unenergized combined) on the densities of red octopus, thin sea pen, and 

white sea urchins. Depths distributions of strata groups are defined under Results in the text.
The Department of the Interior

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