Technical Summary

Study Title: Renewable Energy in situ Power Cable Observation

Report Title: Renewable Energy in situ Power Cable Observation

Contract Number: M11AC00008

Sponsoring OCS Region: Pacific

Applicable Planning Area: Southern California

Fiscal Years of Project Funding: 2011, 2012, 2013

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 Love

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

Address: Santa Barbara, CA 93106

Principal Investigator: Milton Love

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

Background and Objectives

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 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.

Significant Results

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-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).

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, 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.

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.

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, whiteplumed 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, whiteplumed 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.

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.

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