CONTENTS

Introduction.........................................................................................iii

I. Supporting U.S. Obligations of International Agreements....................................1

II. Supporting Pacific Fishery Management Council Activities..............................3

III. Highly Migratory Species Data Coordination.................................................4

IV. Advancing Research on Tunas, Billfish, and Opah.........................................4

V. Advancing Pelagic Shark Research...........................................................14

VI. IDCPA Research................................................................................25

VII. Publications......................................................................................33

i
ii
INTRODUCTION

In The SWFSC Director’s 2012 Report on Research Regarding Highly Migratory Species and 

Their Fisheries in the North Pacific Ocean you will find details of Southwest Fisheries Science 

Center research during the past year (May 1, 2011, to April 30, 2012) relating to tunas, albacore, 

billfishes, oceanic sharks, and protected species associated with their fisheries. The Center’s 

biological, economic, and oceanographic research was focused on supporting the information 

needs of international scientific working groups and committees, the Pacific Fishery 

Management Council, and the National Marine Fisheries Service. Major tuna-related activities 

included stock assessments, socio-economic research, research on interactions between fisheries 

and protected species, population dynamics studies including spatial and temporal modeling of 

fish movements, and life history studies. The data collection and analyses were aimed at 

supporting healthy U.S. and Pacific fisheries, protected marine species, and fish habitat, and 

providing the best available science to help promote effective fisheries management. Significant 

accomplishments from the past year include: completion of a north Pacific albacore stock 

assessment conducted under the ISC and lead by Center scientists that included a new age and 

growth model developed in part with samples provided by our industry partners; tagging and 

tracking the elusive basking shark in the eastern Pacific Ocean; validation of band-pair 

deposition periodicity in vertebrae of juvenile shortfin mako sharks; and conducting alternative 

gear trials to target swordfish below turtle habitat during the day. 

Cisco Werner, Ph.D. 

Director, Southwest Fisheries Science Center

National Marine Fisheries Service

La Jolla, California

May 2012

iii
iv
INTRODUCTION

In The SWFSC Director’s 2012 Report on Research Regarding Highly Migratory Species and 

Their Fisheries in the North Pacific Ocean you will find details of Southwest Fisheries Science 

Center research during the past year (May 1, 2011, to April 30, 2012) relating to tunas, albacore, 

billfishes, oceanic sharks, and protected species associated with their fisheries. The Center’s 

biological, economic, and oceanographic research was focused on supporting the information 

needs of international scientific working groups and committees, the Pacific Fishery 

Management Council, and the National Marine Fisheries Service. Major tuna-related activities 

included stock assessments, socio-economic research, research on interactions between fisheries 

and protected species, population dynamics studies including spatial and temporal modeling of 

fish movements, and life history studies. The data collection and analyses were aimed at 

supporting healthy U.S. and Pacific fisheries, protected marine species, and fish habitat, and 

providing the best available science to help promote effective fisheries management. Significant 

accomplishments from the past year include: completion of a north Pacific albacore stock 

assessment conducted under the ISC and lead by Center scientists that included a new age and 

growth model developed in part with samples provided by our industry partners; tagging and 

tracking the elusive basking shark in the eastern Pacific Ocean; validation of band-pair 

deposition periodicity in vertebrae of juvenile shortfin mako sharks; and conducting alternative 

gear trials to target swordfish below turtle habitat during the day. 

Cisco Werner, Ph.D. 

Director, Southwest Fisheries Science Center

National Marine Fisheries Service

La Jolla, California

May 2012

iii

In The SWFSC Director’s 2012 Report on Research Regarding Highly Migratory Species and 

their Fisheries in the North Pacific Ocean you will find details of Southwest Fisheries Science 

Center research during the past year (May 1, 2011 to April 30, 2012) relating to tunas, albacore, 

billfishes, oceanic sharks, and protected species associated with their fisheries. The Center’s 

biological, economic, and oceanographic research was focused on supporting the information 

needs of international scientific working groups and committees, the Pacific Fishery 

Management Council, and the National Marine Fisheries Service. Major tuna-related activities 

included stock assessments, socio-economic research, research on interactions between fisheries 

and protected species, population dynamics studies including spatial and temporal modeling of 

fish movements, and life history studies. The data collection and analyses were aimed at 

supporting healthy U.S. and Pacific fisheries, protected marine species, and fish habitat, and 

providing the best available science to help promote effective fisheries management. Significant 

accomplishments from the past year include: completion of a North Pacific albacore stock 

assessment conducted under the ISC and led by Center scientists that included a new age and 

growth model developed in part with samples provided by our industry partners; tagging and 

tracking the elusive basking shark in the eastern Pacific Ocean; validation of band-pair 

deposition periodicity in vertebrae of juvenile shortfin mako sharks; and conducting alternative 

gear trials to target swordfish below turtle habitat. 

Cisco Werner, Ph.D.

Director, Southwest Fisheries Science Center

National Marine Fisheries Service

May 2012

La Jolla, California
1

I. SUPPORTING U.S. OBLIGATIONS OF INTERNATIONAL AGREEMENTS

The United States is party to a number of international agreements for the conservation of highly 

migratory species (HMS) in the Pacific Ocean. As such, it is obligated to collect fishery 

statistics from U.S. HMS fisheries and to participate in advancing fishery science for species of 

interest. Scientists at the Southwest Fisheries Science Center (SWFSC) have been tasked to 

fulfill this obligation. In this section, brief descriptions of some of the contributions and 

activities during the past year, May 2011–April 2012, are described.

Monitoring the Purse Seine Fishery in the Western-Central Pacific Ocean – The National 

Marine Fisheries Service (NMFS) collects and manages data from the U.S. purse seine fishery 

for tropical tunas in the western-central Pacific Ocean as part of U.S. obligations under the South 

Pacific Tuna Treaty. Information from U.S. vessels licensed to fish under the treaty is collected 

by the NMFS Pacific Islands Region (PIR) field office in American Samoa and transmitted to the 

SWFSC in La Jolla, California, where information from logbooks, landings and biological data 

from port sampling are processed.

The size of the U.S. purse seine fleet decreased in 2010 to 37 vessels from 39 vessels in 2009. 

Preliminary estimates of the 2010 catch are 246,133 metric tons (t), a decrease of 13% from the 

282,848 t caught in 2009. Skipjack tuna (Katsuwonus pelamis) dominated the catch (88%), 

followed by yellowfin tuna (Thunnus albacares) (10%), and bigeye tuna (T. obesus) (2%). Data 

for 2011 are still being compiled.

Contributing to the Work of the ISC – The United States is a member of the International 

Scientific Committee for Tuna and Tuna-like Species in the North Pacific Ocean (ISC), along 

with Canada, China, Chinese Taipei, Japan, Korea, the North Pacific Marine Science 

Organization, the Secretariat of the Pacific Community, and the Food and Agriculture 

Organization. The purpose of the ISC is to enhance scientific research and cooperation for 

conservation and rational utilization of species of tuna and tuna-like fishes which inhabit the 

North Pacific Ocean, and to establish the scientific groundwork for the conservation and rational 

utilization of these species in the region through a multilateral regime. The ISC is organized into 

five Working Groups—statistics, Pacific bluefin tuna, albacore, billfish and sharks—that meet 

intercessionally and report to a Plenary body. The overall chairman of the ISC is Gerard 

DiNardo of the NMFS Pacific Islands Fisheries Science Center (PIFSC). Results of the ISC are 

made available to participating members and to HMS regional fisheries management 

organizations of the Pacific Ocean.

The 11th ISC Plenary, held in San Francisco 20-25 July 2011, was attended by members from 

Canada, Chinese Taipei, Japan, Korea, Mexico, and the United States. A member of the Western 

and Central Pacific Fisheries Commission (WCPFC) Secretariat attended as an observer. PIFSC 

Director Sam Pooley led the U.S. delegation at this meeting.

Key Results of the 11th Meeting – The Plenary reviewed results and conclusions, which were 

based on new data and updated analyses, of the albacore tuna, billfish, and Pacific bluefin tuna 

working groups. The Plenary endorsed the findings that the albacore stock was not experiencing 

overfishing and that the stock is likely not in an overfished condition. It further recommended 
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that the fishing mortality rate on albacore (Thunnus alalunga) tuna not be increased. Regarding 

Pacific bluefin tuna (T. orientalis), striped marlin (Tetrapterus audax), and North Pacific stocks 

of swordfish (Xiphias gladius), the Plenary maintained the conservation advice of ISC10 with 

minor changes for clarification. The Plenary endorsed the work plan of the shark working group 

and the prioritized list of ISC shark species of interest, blue (Prionace glauca) and shortfin mako 

(Isurus oxyrinchus) sharks, was ranked high priority. A special seminar on Best Available 

Scientific Information was held – concepts from which ISC will incorporate into its Operations 

Manual. The ISC work plan for 2011-2012 includes completing a new stock assessment for 

striped marlin and Pacific bluefin tuna by ISC12, continuing preparation for a Pacific blue marlin 

(Makaira nigricans) stock assessment in 2012, preparations for an updated blue shark stock 

assessment in 2012/2013, implementing improved database and website management, and 

conducting a peer review of its structure. After three years serving as vice chairman of ISC, 

Michel Dreyfus stepped down. The Plenary elected Chi-Lu Sun to serve as vice chairman for 

2011-2014. The next Plenary will be held in Japan in July 2012. 

Albacore Stock Assessment and Research – The commercial surface albacore fishery is the 

most important fishery for HMS on the U.S. West Coast. In June 2011, SWFSC researchers led 

an assessment of the status and trends in the North Pacific albacore stock, as members of the ISC 

Albacore Working Group (ALBWG), at a meeting in Shimizu, Japan. The assessment was 

conducted using fishery data through 2009 and a seasonal, length-based, age-structured Stock 

Synthesis (SS3) model. Based on this assessment, the North Pacific albacore stock is considered 

not to be overfished and overfishing is not occurring. 

The assessment model used quarterly catch and size composition data, with 16 defined fisheries, 

eight abundance indices, and conditional age-at-length (otolith aging) data. One of the most 

important changes with respect to previous assessments is a change in the growth curve for the 

stock. A fixed growth curve from Yabuta and Yukinawa (1963) was used in previous 

assessments. However, a recent study by SWFSC scientists in collaboration with Japanese 

scientists from the National Research Institute of Far Seas Fisheries (Wells et al., 2011) showed 

that the Yabuta and Yukinawa (1963) growth curve was not representative of the North Pacific 

albacore stock. Otolith aging data from Wells et al. (2011) was employed for this assessment,

and the growth curve was estimated within the assessment model, which resulted in a more 

representative growth curve and improved fits to the length composition data. Most importantly, 

the L∞ was estimated to be 118 cm rather than the 146.6 cm from Yabuta and Yukinawa (1963).

The base-case model estimates that spawning stock biomass (SSB) has likely fluctuated between 

300,000 and 500,000 t between 1966 and 2009, and that recruitment has averaged approximately 

48 million fish annually during this period. Fishing mortality (F-at-age) increases to its highest 

level on 3-year-old juvenile albacore and then declines to a much lower and stable level in 

mature fish. Current fishing mortality (F2006-2008) is lower than F2002-2004 (current F from the 2006 

assessment) and is about 71% of FSSB-ATHL, which means F is below the fishing mortality that 

would lead SSB to fall below the average of the ten historically lowest estimated SSBs (SSBATHL) threshold. Estimates of F2006-2008 expressed as a ratio relative to several potential F-based 

reference points (FMAX, F0.1, FMED, F20-50%) are also less than 1.0. It is based on these findings

that the ALBWG concluded that overfishing is not occurring and the stock is not in an overfished 

condition.
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In addition to the stock assessment, SWFSC scientists are also involved in several studies that 

will improve our understanding of the population dynamics and biology of North Pacific 

albacore. Importantly, SWFSC scientists recently published a paper (Childers et al., 2011) in the 

journal Fisheries Oceanography on the “Migration and behavior of juvenile North Pacific 

albacore (Thunnus alalunga),” which describes the results of our long-term, electronic tagging 

experiment. SWFSC scientists, in collaboration with PIFSC and Canada’s Department of 

Fisheries and Oceans (DFO) scientists, have also recently received funding from NOAA's 

Fisheries and the Environment (FATE) program, to study the “Influence of the North Pacific 

Current on the spatial distribution and availability of North Pacific albacore in the northeast 

Pacific Ocean.” We expect to develop (1) an environmental time series that indicates albacore 

availability to U.S. surface fisheries and (2) integrate the time series into future stock assessment 

models. 

Bluefin Tuna Stock Assessment and Research – Pacific bluefin tuna was historically an 

important commercial fishery for HMS on the U.S. West Coast. In recent years, however, the 

primary U.S. fishery targeting this species has been the U.S. sport fishery operating out of San 

Diego, California. There remains an important commercial fishery for Pacific bluefin tuna in 

Mexican waters. 

As members of the ISC Pacific Bluefin Working Group (PBFWG), SWFSC researchers are 

preparing for a full stock assessment of Pacific bluefin tuna scheduled for June 2012. The 

PBFWG currently uses a length-based, age-structured Stock Synthesis model for stock 

assessments. In January 2012, SWFSC scientists met with fellow members of the PBFWG in La 

Jolla to discuss data inputs and model specifications for the upcoming assessment. At a previous 

PBFWG meeting, SWFSC researchers demonstrated the detrimental effects of assessment model 

misfits to eastern Pacific Ocean (EPO) time-series. The PBFWG therefore decided to not fit the 

assessment model to EPO abundance indices in the upcoming assessment. In addition, SWFSC 

researchers also developed a SS3-VPA hybrid model and a SS3 model incorporating transPacific movements as research tools to help improve future assessment models. A manuscript on 

the SS3-VPA model entitled “A hybrid Stock Synthesis-Virtual Population Analysis model of 

Pacific bluefin tuna” is currently under review. 

II. SUPPORTING PACIFIC FISHERY MANAGEMENT COUNCIL ACTIVITIES –

Center scientists Stephen Stohs and Suzanne Kohin continued serving on the Highly Migratory 

Species Management Team (HMSMT) of the Pacific Fishery Management Council (PFMC) over 

the past year. Stohs served as HMSMT chair from April 2009 through 2012. The chairmanship 

was passed to a team member from Washington Department of Fish and Wildlife in January 

2012, but Stohs still plays a leadership role with respect to Federal input to the team. The team 

met several times in 2011 and early 2012 to review fishery information, complete assignments 

from the Council and evaluate provisions of the Fishery Management Plan for U.S. West Coast 

Fisheries for Highly Migratory Species. 

The main HMS issues facing the team and the Council over the past year have been (1) assisting 

the Council with providing recommendations on international HMS fishery management issues 
4

to the U.S. delegations of the WCPFC and Inter-American Tropical Tuna Commission (IATTC); 

(2) participating in and reporting to the Council on activities relevant to west coast swordfish 

fisheries, including a two-day informational meeting held with stakeholders in San Diego during 

May 2011; (3) providing updates to the Council and its advisory bodies on the status of North 

Pacific albacore following completion of the 2011 assessment and helping to develop an 

albacore management framework for West Coast fishers; (4) working with state, PacFIN, and 

RecFIN representatives to tackle ongoing data management discrepancies; and (5) preparing the 

2011 Stock Assessment and Fishery Evaluation (SAFE) Report and planning for the 2012 SAFE 

Report.

III. HIGHLY MIGRATORY SPECIES DATA COORDINATION - The PIFSC, PIR, 

Southwest Region (SWR), and SWFSC share reporting obligations for HMS fisheries in the 

Pacific. Staff from each office collaborate to meet the international reporting obligations to 

Regional Fisheries Management Organizations (RFMOs), Councils and other customers and 

provide HMS data summaries required by these reporting obligations. Staff from each office 

routinely exchange information needed for various reports, data submissions, and other reporting 

purposes such as informal data requests. Formal annual meetings of the staff members have not 

occurred since 2005, though ad hoc meetings and correspondence continue.

HMS staff participate in the Fisheries Information System (FIS) based at NMFS headquarters. A 

representative from SWFSC, SWR, PIFSC, and PIR is on the FIS Program Management Team,

which directs FIS-sponsored projects and activities. FIS funds numerous projects that contribute 

toward improving fisheries-dependent data that are collected and maintained by the agency and 

partner organizations. Staff members from SWFSC, SWR, PIFSC, and PIR are leading several 

of these projects to improve data collection and management systems in their respective regions.

HMS information technology specialists at the SWFSC are also improving data collection 

methods. Current and past electronic data collection and monitoring projects include data 

monitoring systems for regional observer programs, electronic calipers and handheld computers 

used to collect length measurements, and electronic logbook software applications. These 

monitoring and collection methods increase the data quality and timeliness of reporting while 

reducing operational costs and easing reporting burdens on fishermen. In addition, web-based 

reporting systems continue to be developed by SWFSC staff, improving the quality and 

availability of information collected in remote locations.

IV. ADVANCING RESEARCH ON TUNAS, BILLFISH, AND OPAH

The SWFSC research on tunas and billfishes in the Pacific Ocean has largely been focused on 

improving our understanding of the biology and ecology of the animals to support needs for 

assessing the effects of fishing and environment on the population or stock. Described below are 

studies that have been recently completed or are ongoing by Center staff. These studies are 

carried out largely in cooperation with stakeholders and in collaboration with colleagues both in 

the U.S. and abroad.

Monitoring the U.S. Albacore Troll and Pole-and-Line Fishery – U.S. troll and pole-and-line 

vessels have fished for North Pacific albacore since the early 1900s and for South Pacific 
5

albacore since 1986. North Pacific albacore fishing areas range from Vancouver Island to the 

coast of Baja California and from the U.S. West Coast to approximately 160°E. The fishing 

season begins in late April and can last into mid-November. The size of the troll fleet for a 

season ranges from 500 vessels to more than 1,000 vessels. Approximately 632 U.S. troll and 

pole-and-line vessels fished for North Pacific albacore in 2010. The total albacore catch in 2010 

was 12,661 t, a slight decrease from the 12,793 t caught by vessels in 2009. Data for the 2011 

season are currently being compiled.

Fishing areas for South Pacific albacore extend eastward from the east coast of New Zealand to 

approximately 110°W and between 30°S to 45°S, overlapping the jurisdictional areas of two 

RFMOs. This fishery begins in late December and continues until early April of the following 

year. The international troll fleet in the South Pacific consists of 5 to more than 50 vessels. 

Factors such as increased fuel costs, lower ex-vessel prices and reduced availability of fish have 

contributed to a decrease in participation in the South Pacific troll fishery in recent years. Only 6

U.S. troll vessels fished for albacore in the South Pacific during the 2009-2010 season; they 

caught 237 t of albacore, an increase from 150 t caught the previous season by 4 vessels. 

Bycatch species are sometimes reported in vessel logbooks and include yellowtail, dolphinfish

(Coryphaena hippurus), and skipjack, as well as yellowfin, bigeye, and bluefin tunas.

Cooperative Research with the U.S. Surface Albacore Fishery – SWFSC scientists are 

working with the American Fishermen’s Research Foundation (AFRF) and the American 

Albacore Fishing Association on monitoring programs and other research efforts to improve 

knowledge of the biology and migration of North Pacific albacore in the waters off the U.S. 

Pacific coast. The cooperative research is described below.

North Pacific Albacore Biological Data Sampling Program – Since 1961, a biological data 

collection program, or port sampling program, has been in place for collecting size data from 

albacore landings made by the U.S. and Canadian troll fleets at ports along the U.S. Pacific 

coast. State fishery personnel collect the biological data by following sampling and data 

processing instructions provided by the SWFSC, where the database is maintained. In recent 

years, with AFRF support, fishermen have also collected biological data during selected fishing 

trips. These data are collected to augment data collected through the port sampling program. 

Following procedures established by SWFSC scientists, fishermen on 5 vessels measured 1,010 

albacore during the 2010 season. During 2011, 2 vessels measured 1,939 fish. The sample 

information provided by the fishermen helped to fill in gaps missed by the port sampling 

program. Overall, the sizes were found to be generally similar to those collected through the port 

sampling program.

North Pacific Albacore Archival Tagging Project – The SWFSC and AFRF initiated an archival 

tagging program in 2001 to study the migration patterns and stock structure of juvenile albacore 

in the North Pacific. Since 2001, a total of 720 archival tags and 43 dummy tags have been 

deployed. Two tagging trips were conducted during 2011, both off northern Oregon aboard the 

chartered F/V Royal Dawn: 1-6 August, during which 39 tags were deployed and 5-9 October 

with an additional 51 tags deployed. This is the greatest tagging effort since 2006, and plans are 

being made to similarly deploy over 100 tags during the 2012 season. During 2011, no 

additional tag recaptures were reported. 

7

Bertalanffy (VB) model provided the best fit (Fig. 1). Biological parameters of the specialized 

VB model included L∞=124.1, K=0.164, and t0=-2.239. Daily ages of several age-1 fish (55-61 

cm FL) were also determined and confirmed correct annual age class assignments, with daily 

ages ranging from 378 to 505 days. In addition to otolith-based techniques, dorsal fin spines and 

length frequency (LF) analysis were used to generate estimates of size-at-age. Fin spine ages 

generally matched otolith-derived ages (85% of samples), though samples were only available 

and analyzed for young fish. Results of the VB growth model generated from LF analysis 

provided similar size-at-age for the first five age classes but estimated smaller sizes for fish ages 

6 to 9, which may be a product of the limited size distribution from fishery-dependent data. 

Results suggest North Pacific albacore are a relatively long-lived tuna species and provide 

updated biological parameters useful for future stock assessment models incorporating agespecific life history information.

Population Structure – Population structure of North Pacific albacore appears to be more 

complex than the current single stock hypothesis given the apparent regional differences in 

growth rates and movement patterns in the EPO. Accurately characterizing population structure 

and stock mixing is critical to effective management. Otolith chemistry is one approach to 

investigate population structure of tunas and other fish. The principal assumption is that the 

otolith acts as a natural tag because the chemical composition of the otolith is related to the 

physicochemical conditions of the water mass inhabited. As such, the purpose of this study is to 

examine otolith stable isotopes of carbon (δ13C) and oxygen (δ18O) in addition to several trace 

elements in whole otoliths of albacore collected in the northern region (offshore Oregon and 

Washington, > 40°N) and southern region (offshore Southern California and northern Baja 

California, Mexico, < 40°N). Samples from three age classes (ages 2-4) were collected from 

each region through recreational and commercial fisheries from during the 2010 and 2011 

seasons. Significant differences existed in otolith chemistry from fish collected between the two

regions (P < 0.05) and overall cross-validated classification success was 100%, with age-specific 

comparisons exceeding 90% success. Otolith δ18O was significantly enriched in the southern 

region relative to the northern region, similar to reported seawater δ18O differences. In addition, 

significantly higher concentrations of sodium and magnesium, combined with lower phosphorus 

in otoliths from fish collected in the southern region, is consistent with regional physicochemical 

conditions (i.e., salinity, temperature, phosphate). Our findings support previous studies that 

have shown limited regional mixing of albacore in the EPO and provide life history information 

useful for management of North Pacific albacore.

Biological Sampling of Tunas in the Eastern Pacific Ocean – Tunas in the EPO, including the 

waters off the U.S. and Mexico, support substantial commercial and recreational fisheries and are 

also important components of the local food web. To better understand their basic biology and 

ecological role in the EPO, the SWFSC and the Sportfishing Association of California initiated a 

biological sampling program in 2007 to collect data on tuna and other HMS. While initially the 

program was focused in the Southern California Bight (SCB), in 2009 the program was 

expanded to the northeast Pacific Ocean working with commercial fishermen to collect samples 

from albacore off Oregon and Washington (see above). Utilizing the commercial passenger 

fishing vessels (CPFV), commercial albacore troll/baitboat fleet, and recreational anglers based 

out of San Diego and SWFSC research cruises, we have collected samples from albacore, 

bluefin, yellowfin, skipjack, opah (Lampris guttatus), and dorado (Coryphaena sp.) (Table 1). In 

9

Stable isotope analyses of muscle tissues are currently being used to help characterize trophic 

relationships between prey and predators in the SCB. The California Current is known as a 

highly productive eastern boundary current, and researchers have suggested that these are waspwaist systems with low diversity at mid-trophic levels. This low diversity of prey for top 

predators had been linked to dramatic bottom-up effects associated with variability in mid-level 

prey species. Estimates of trophic level are being used to evaluate links between prey and 

predators in regards to wasp-waist dynamics. Preliminary results suggest predator-prey 

relationships in the SCB are more complex than would be predicted in a wasp-waist system, with 

a high degree of diversity and omnivory in predator diets. Consequently, predators in the SCB

should be more resilient to prey variability than would be suggested under a wasp-waist model. 

In addition to studying the HMS themselves, the predators can be used as biological samplers 

and provide a snapshot of the forage base. Linking changes to environmental factors that 

influence the recruitment, distribution, and resulting availability of forage prey types may reveal 

insight about habitat quality and migration patterns of HMS in the California Current. By 

sampling over multiple years we are gaining insight into the impacts of climate variability on 

local prey and predators which will help us to predict the impacts of climate change on the 

California Current ecosystem. 

Cooperative Research with Billfish Anglers – The SWFSC and billfish angling community have 

been working together since 1963 to study various aspects of billfish biology and to obtain an index 

of angler success in the Pacific Ocean. This collaboration has resulted in one of the longest timeseries available for recreational billfishing, charting trends in catch-per-unit-effort (CPUE) for key 

species. The research has also included recreational and commercial fishery monitoring, stock 

assessments efforts, biological research into the life history and ecology of specific billfish 

species, and determining the economic importance of billfish resources. Two major components 

of the cooperative research that were the focus in 2011 were the International Billfish Angler 

Survey and the Billfish Tagging Program. 

International Billfish Angler Survey – In 2011, SWFSC researchers summarized the results 

from the 2010 Billfish Angler Survey. Initiated in 1969, the survey now provides a 42-year time 

series of billfish angling effort and catch in the Pacific Ocean. The time series of angler success 

provides a measure of relative abundance and is the only fisheries-independent survey in the 

Pacific. CPUE, measured in number of billfish caught per angler fishing day across all reporting 

areas in the Pacific, was 0.44 in 2010. This CPUE is slightly lower than that reported in 2009 

(0.46) and well below the most recent 5-year average (2005-2009; 0.66). CPUE time series were 

examined individually for the main species caught [Pacific blue marlin, striped marlin, Pacific 

sailfish (Istiophorus platypterus), and black marlin (Makaira indica)] in the main fishing areas 

(Tahiti; Hawaii; Baja California, Mexico; Southern California; Guatemala; Costa Rica; Panama;

and Australia; Fig. 2). The CPUE for several species was lower in locations where they are 

commonly targeted. Blue marlin CPUE off Hawaii was 0.22, which was above average but a 

decrease from the previous two years. Blue marlin CPUE off Baja California, Mexico, was 0.07 

in 2010, which is the median catch rate for this area. Striped marlin CPUE off Southern

California was the lowest on record (0.03). Despite an increase in reported catch throughout 

Mexico, a drop in striped marlin CPUE was also reported from Baja California. La Niña 

conditions brought cold waters to these areas from July through October and may have 

11

recapture data are used to determine movement and migration patterns, species distribution, and 

age and growth patterns. This volunteer tagging program depends on the participation and 

cooperation of recreational anglers, sportfishing organizations, and commercial fishers. Since its 

inception, more than 62,000 fish of 75 different species have been tagged and released. 

Emphasis continues to be on the skillful tag and release of billfish. A total of 416 tags were 

released on billfish in 2010 through the efforts of over 300 anglers and 95 captains. 

Unfortunately, the 2010 tag release total is down from recent years and may reflect a decrease in 

fishing effort by our constituents. Indeed, 2010 had the highest percentage of anglers reporting 

“no fishing” in the International Billfish Angler Survey. Fortunately, preliminary reports 

indicate the tagging effort increased substantially in 2011. Table 2 shows the tagging effort for 

2010 and tag recoveries throughout the program’s history. The data include releases made by 

SWFSC scientists during research cruises.

Swordfish Research and SLUTH – Since 2006, NMFS has been studying swordfish in the SCB 

to examine migratory patterns, foraging ecology, and local stock structure. In 2008, researchers 

in the SWFSC’s Fisheries Resources Division (FRD) teamed up with the Protected Resources 

Division (PRD) and the SWR to launch a new initiative, Swordfish and Leatherback Use of 

Temperate Habitat (SLUTH). The overarching objective of SLUTH is to integrate studies of 

swordfish and leatherback sea turtles to inform management and conservation efforts. The 

endangered leatherback is taken incidentally in swordfish fisheries, and concerns about 

leatherback populations are currently shaping the management of swordfish fisheries along the 

U.S. West Coast. The first step in this process was a stakeholder workshop that was conducted 

in May 2008. A report detailing the content and discussions of the workshop was published as 

an Administrative Report in 2009 (Benson et al., 2009; LJ-09-06). While a large organized 

initiative has yet to be established, FRD and PRD have a number of ongoing research projects to 

characterize the habitat of swordfish and leatherback sea turtles to identify where habitat 

separation is maximized in time and space. Information on habitat separation can be used to 

increase the selectivity of fisheries and to reduce bycatch. 

Characterizing Target Catch and Non-target Species Catch and the Behavior of Fishermen –

Part of the SLUTH initiative is to explore creative methods to reduce the bycatch of non-target 

species in the California drift gillnet fishery (CADGN). One approach is to use the fisheries data 

to better understand the environmental factors that affect the distribution of leatherbacks, 

swordfish, and the fishers themselves. Working together, researchers from the PRD and FRD 

are using novel statistical approaches including boosted regression trees and random forests to 

model the relationships between the distribution and abundance of the focal species, fishing 

effort, and a range of factors. The first approach has been to characterize the impact of 

environment on catch rates. Results indicate that catch rates respond to both biotic (primary 

production, zooplankton abundance) and abiotic (sea surface temperature or SST, currents, 

depth) factors. If combined with data on location (i.e., latitude/longitude) and time of year (i.e., 

month), these factors can be used to predict swordfish catch rates with impressive accuracy (e.g., 

cross validated R2 of ~ 0.7). A manuscript covering this research is in preparation for the ICES 

Journal of Marine Science. A second approach is to use the fisheries data to better understand the 

factors that affect the distribution of fishing effort. Patterns in bycatch may be more directly 

linked to fishing effort rather than target species. Many factors other than target species 

distribution can influence where fishers fish, for example vessel size, distance from shore, and 
12

home port. Our results suggest that it is possible to accurately predict fishing effort using a 

modest set of readily available predictor variables. Thus, with information on bycatch species 

distributions we could forecast where the probability of bycatch is high and make adjustments in 

advance. A manuscript on this research is ready for submission to the journal Conservation 

Biology.

Table 2. Summary of fish tagged through the Billfish Tagging Program in 2010 with releases 

and recoveries for 1963–2010, including SWFSC’s ongoing research tagging.

SPECIES NAME RELEASE 

2010

RELEASE 

TOTAL

RETURN 

TOTAL

RETURN 

RATE (%)

Striped Marlin 43 22934 345 1.50

Pacific Blue Marlin 307 10765 90 0.84

Sailfish 22 9201 49 0.53

Billfish, unidentified 9 4386 6 0.14

Black Marlin 2 3387 69 2.04

Shortfin Mako Shark 56 2303 217 9.42

Shortbill Spearfish 33 2145 2 0.09

Blue Shark 196 1226 126 10.28

Common Thresher Shark 274 1330 78 5.86

Broadbill Swordfish 0 521 17 3.26

Yellowfin Tuna 0 349 25 7.16

Skipjack Tuna 0 100 2 2.00

Albacore Tuna 33 749 29 3.87

Bigeye Tuna 0 79 0 0.00

Bluefin Tuna 0 58 2 3.45

Bronze Whaler Shark 0 51 3 5.88

Hammerhead Shark 0 55 2 3.92

Leopard Shark 0 45 8 17.78

Whitetip Shark 0 44 1 2.33

Soupfin Shark 0 33 1 3.03

Atlantic Blue Marlin 0 43 0 0.00

Salmon Shark 0 33 3 9.09

Silky Shark 0 21 0 0.00

White Marlin 0 13 1 7.69

Basking Shark 0 7 0 0.00

Longbill Spearfish 0 3 0 0.00

Other Tunas 0 21 1 4.76

All Others 3 2538 114 4.49

TOTAL 978 62440 1191 1.92

Improving Location Estimates from Electronic Tags – In addition to characterizing swordfish 

habitat using catch data, electronic tags are also being used. While the traditional pop-up 

satellite tags provide valuable information on vertical behavior, obtaining an accurate assessment 

of location is made challenging by the diel vertical migrations of swordfish. We are currently 

working with a researcher at CSIRO (Commonwealth Scientific and Industrial Research 

Organisation) in Australia on software to improve light-based geolocation estimates. The novel 
13

approach treats the data as sequentially independent decisions instead of constructing a track. 

This allows us to concentrate on the analysis of covariates describing the movement instead of 

estimating a model describing the full path of the animal. This approach will be used to 

characterize the impacts of environment on both large-scale and vertical movements. In 

addition, the code will be further developed for use with other tag types. This type of approach 

will improve our ability to understand and predict movements and consequently overlap with 

protected species. 

Opah Research in the Eastern Pacific Ocean – The opah is a large, mid-water pelagic fish that 

occurs seasonally in the SCB. While they are not targeted, they are taken incidentally in both 

local recreational fisheries for tuna and the CADGN fishery targeting swordfish. In recent years 

opah has become increasingly popular in seafood markets. Despite their value to commercial 

and recreational fishermen, little research on the basic biology and ecology of opah has been 

conducted, especially in the SCB. For example, there is little data on foraging ecology, size 

composition in fisheries, essential habitat, and stock structure. To begin to fill some of the data 

gaps, in 2009 the SWFSC began collecting biological samples from opah caught and initiated an 

electronic tagging program in 2011. 

Incidental Take of Opah in the Southern California Bight – Based on a preliminary analysis of 

the CADGN observer database, covering the years from 1990 to 2005, catch rates were relatively 

consistent across years, averaging 0.53 opah per set. Peak catch rates were observed in 1997 (1.2 

opah per set) during El Niño oceanographic conditions. This is similar to a reported increase in 

opah landings during the1982-83 El Niño and suggests that the SCB may be towards the 

northern extent of the core of the opah’s range. After 2005 there appears to have been an 

increase in catch rates, with the average from 2006-2010 at 1.6 opah per set. For comparison,

the catch rate for swordfish from 1990-2010 was 2.1 per set. If recent trends persist, opah could 

become a more important component of the fishery. Further evaluation of observer and logbook 

data from the CADGN needs to be conducted to determine whether the variability is related to 

abundance, availability, fishing practices, or environmental conditions.

Opah Foraging Ecology – Over the past three years, stomachs have been collected from 28 

opah. Preliminary analysis of 10 stomachs revealed a total of 19 species, including hake, 

barracudinas, and Octopodoteuthis, with cephalopods making up 5 of the 7 most important prey 

species. Based on the data collected to date, opah appear to feed primarily on species associated 

with the DSL. This is consistent with their diel migrations that are similar to those of swordfish 

that also feed on the DSL. A previous study in the central North Pacific also found that 

mesopelagic prey species dominated opah diet composition. A comparison with diets of tunas 

and swordfish from the SCB suggests greater niche overlap with swordfish than with tunas. 

Considering that opah are often caught in association with tunas, the differences in their diets 

could reflect habitat partitioning.

Electronic Tagging – To help characterize the vertical and horizontal movements of opah in the 

SCB, two Wildlife Computers PSAT-Mk10 tags were deployed on opah in October 2011 during 

a research longline cruise conducted by the SWFSC. This is the first time an opah has been 

tagged in the EPO. The PAT tags were programed to collect light, depth, and temperature data 

for 240 days and then to release from the fish. One tag reported back to the Argos satellite 
14

Figure 3. Histogram showing the depth distribution of an 

opah tagged off of California during both daytime (yellow) 

and nighttime (dark blue) hours. 

prematurely. For the first 21 days 

of the record, behaviors were 

similar to those reported off Hawaii. 

While the opah remained below the 

mixed layer, they exhibited a deep 

diel migration (Fig. 3). At 21 days 

it appears that the opah was ingested 

by an endothermic predator. The 

tag was ultimately expelled and 

came to the surface where logged 

data were transmitted to satellite. 

The second tag is still at liberty. 

Additional tags will be deployed in 

2012 to further examine their 

habitat use and migratory patterns in

the EPO.

Gill Morphology – In 2011, three sets of opah gills were preserved in 10% formalin and 

transported to the SWFSC for examination and comparison to other pelagic fishes. 

Determination of gill surface area and associated dimensions allows for insights into both the 

metabolic requirements and dissolved oxygen concentrations experienced by this species. In 

addition to a number of morphometric similarities with other pelagic fishes, opah gills show 

extensive fusion of the gill filaments, a characteristic previously documented only in highperformance teleosts (tunas of the genus Thunnus, the wahoo, Acanthocybium solandri, and 

billfishes). The occurrence of filament fusions in opah suggests a role other than that proposed 

for the high-performance fishes, which use gill fusions to maintain optimal gill orientation and 

reduce branchial flow rates during ram ventilation. Opah are not thought to be obligate ram 

ventilators, but like tunas are active predators.

V. ADVANCING PELAGIC SHARK RESEARCH

The SWFSC’s shark research program focuses on pelagic sharks that occur along the U.S. 

Pacific coast, including shortfin mako, blue sharks, basking sharks (Cetorhinus maximus), and 

three species of thresher sharks: common thresher (Alopias vulpinus), bigeye thresher (A. 

superciliosus), and pelagic thresher (A. pelagicus). Center scientists are studying the sharks’ 

biology, distribution, movements, stock structure, population status, and potential vulnerability 

to fishing pressure. This information is provided to international, national, and regional fisheries 

conservation and management bodies having stewardship for sharks. Some of the recently 

completed and ongoing shark research activities being carried out at the SWFSC are discussed 

below.

Abundance Surveys – The blue, shortfin mako, and thresher sharks are all taken in regional 

commercial and recreational fisheries. Common thresher and mako sharks have the greatest 

commercial value and are also specifically targeted by sport fishers, especially off Southern

California. Although the blue shark is targeted in Mexico, it has little market importance in the 

U.S. but is a leading bycatch species in the CADGN and high-seas longline fisheries. Although 
15

catches of adult blue, thresher, and shortfin mako sharks do occur, the commercial and sport 

catch of these species off Southern California consists largely of juvenile sharks. 

To track trends in the abundance of juvenile and subadult blue and shortfin mako sharks and 

neonate common thresher sharks, surveys are carried out in the SCB each summer. Efforts to 

determine abundance trends from commercial fishery data have been complicated by changes in 

regulations, targeted areas, and fishing methods over time. These changes have resulted in 

inconsistent capture rates and catch distributions that are difficult to interpret. Therefore, 

fishery-independent sampling was initiated, with slightly different survey strategies required 

depending upon the species.

Offshore longline surveys from relatively large research vessels have proved most effective for 

sampling and estimating abundance trends of the more oceanic shortfin mako and blue sharks. 

For mako sharks, the surveys have enabled the SWFSC to obtain a valuable abundance index, 

which can be linked to a historical time series of logbook and landings data from a former 

experimental shortfin mako longline fishery in the SCB that occurred during 1988-1991. 

Abundance trend information is also obtained for the blue shark, which is compared to that 

obtained by observers of the CADGN and U.S. and Japanese high-seas longline fisheries. 

Surveys for neonate thresher sharks are conducted using a small commercial longline vessel. 

Initial studies demonstrated that neonate threshers are rarely encountered in waters deeper than 

about 90 m. Therefore, surveys are conducted in the shallower nearshore waters between Point 

Conception, California, to the north and the U.S.-Mexico border to the south. The primary 

purpose of the surveys is to produce a relative abundance index for the West Coast population by 

periodically sampling 0-year pups (neonates) in their nursery grounds off Southern California. 

Representative areas were initially identified and are now sampled annually. The resulting 

neonate index of abundance should mirror adult abundance because adult population and 

recruitment should be tightly linked in K-selected species such as sharks. This study 

complements the fishery-dependent data available through the nearshore small mesh net fisheries

and offshore CADGN fishery to provide measures of relative abundance of common thresher 

sharks for stock assessment models. 

Juvenile Mako and Blue Shark Survey – In 2011, the SWFSC conducted its eighteenth juvenile 

shark survey for mako and blue sharks since 1994. The annual abundance survey was completed 

between 24 June and 13 July 2011. Working aboard F/V Ventura II, a team of scientists and 

volunteers fished a total of 5,493 hooks during 27 daytime sets inside seven focal areas within 

the SCB. Survey catch totaled 61 shortfin makos, 49 blue sharks, 5 pelagic rays 

(Pteroplatytrygon violacea), 4 opah, and 1 common mola (Mola mola). The preliminary data 

indicate that the nominal survey catch rate was 0.28 per 100 hook-hours for shortfin mako and 

0.22 per 100 hook-hours for blue sharks. The nominal CPUE for both blue and shortfin mako 

sharks were slightly higher than for the previous year. However, while more detailed analyses 

are needed, there is a declining trend in nominal CPUE for both species over the time series of 

the survey (Fig. 4). 
16

Figure 4. Average (± standard error) catch and temperature per survey set for shortfin mako and 

blue sharks, 1994 – 2011. No data were collected in 1998 and 1999. Blue shark catch per 100 

hook-hours was 7.37 in 2000.

Additional research projects were also conducted after the shark survey was completed. The 

ship re-deployed 21-30 October 2011. The first goal of the final leg was to develop and test the 

potential for setting a longline deep during the day in order to catch and tag swordfish to study 

their fine-scale habitat-use patterns. The second goal was to troll for small tunas to deploy 

archival tags and collect biological samples. Eleven deep longline sets and many hours of 

trolling were conducted in an area west of Point Conception and offshore up to Central 

California. All fish caught were documented and released with or without tags or retained for 

biological sampling. Three swordfish were caught and one was tagged with a satellite tag. Two 

opah were also tagged. The three species that comprised the majority of the catch were blue 

sharks (n=105), albacore (n=25, 23 of which were caught while trolling), and opah (n=10). A 

total of 97 blue sharks were tagged with conventional tags. A number of rare deepwater species,

such as the king-of-the-salmon (Trachipterus altivelis), were also caught. 

During the combined summer and fall HMS cruise, 48 longline sets and over 30 hours of trolling 

were completed. A total of 474 fish were caught. Ancillary sampling, including trolling, 

resulted in 353 captures, which was nearly 75% of the total catch. Many of the captures outside 

of survey blocks were juvenile blue sharks caught near the Mexican border (~32°N, 118.2°W). 

In 2011, 14 opah were caught, in comparison to 16 in 2010 and 8 in 2009. Prior to 2009, only 

one other opah had been recorded during a longline survey cruise, in June of 2000. A total of 

366 conventional spaghetti tags were released on sharks for movement and stock structure data. 

A total of 452 DNA samples were collected, including samples from 315 blue sharks, 68 shortfin 

makos, 25 albacore, 12 opah, 9 skipjack, 7 bluefin tuna, 4 Pacific pomfret (Brama japonica), 4 

lancetfish, 3 king-of-the-salmon, 3 pelagic rays, 3 swordfish, and 1 common thresher. 

In a cooperative effort with TOPP (Tagging of Pacific Pelagics), a total of 7 electronic tags were 

deployed on sharks to examine the habitat-use patterns in the California Current System. Two 

shortfin mako sharks (182 and 235 cm FL) and four blue sharks (161, 164, 169, 171, and 226 cm 

FL) were released with radio position transmitting (SPOT) tags (see below). 
17

Neonate Common Thresher Shark Survey – In 2011, the SWFSC team conducted the survey 

aboard the F/V Outer Banks. Forty-seven longline sets were made in relatively shallow, 

nearshore waters and a total of 4,800 hooks were fished during the 18-day cruise. A total of 556 

fish including a range of species were sampled during the survey. Three hundred and ninety-one 

(391) common thresher sharks were tagged with conventional tags for movement and stock 

structure data and 409 DNA samples were collected. 

The preliminary survey data indicate that the average nominal catch rate by set was 5.57 per 100 

hook-hours for common thresher sharks. This is the highest catch rate since the inception of the 

sampling program. The distribution of common threshers is very patchy and areas of high 

abundance are not consistent across years. In all years, a large percentage of the catch has been 

neonates, which were found in all areas surveyed. In addition to providing important information 

on abundance and distributions, the thresher shark pre-recruit survey enhances other ongoing 

research at SWFSC, including age and growth, feeding, and habitat utilization studies.

Electronic Tagging Studies – Since 1999, NOAA (National Oceanic and Atmospheric 

Administration) has been using satellite technology to study the movements and behaviors 

primarily of blue, shortfin mako, and common thresher sharks, while other species are tagged 

opportunistically. In recent years, shark tag deployments have been carried out in collaboration 

with Mexican colleagues at CICESE (Centro de Investigación Científica y de Educación 

Superior de Ensenada), and Canadian colleagues at the DFO Pacific Biological Station in 

Nanaimo, British Columbia, and the TOPP program (www.topp.org). The goals of the projects 

are to document and compare the movements and behaviors of these species in the California 

Current and to link these data to physical and biological oceanography. This approach will allow 

us to characterize the essential habitats of sharks and subsequently to better understand how 

populations might shift in response to changes in environmental conditions on short or long time 

scales. 

In 2011, 2 shortfin mako sharks, 5 blue sharks, and 2 basking sharks were tagged with either 

SPOT tags or towed GPS tags. Since 1999, a total of 97 makos, 90 blue sharks, 28 common 

threshers, 2 hammerheads, and 3 basking sharks have been satellite tagged through collaborative 

projects.

SPOT tags continue to provide excellent information on the movements of blue and mako 

sharks, and we now have a decade worth of data for both species. Of the 5 tags deployed on blue 

sharks, those deployed on smaller sharks (~165 cm FL) lasted for an average of 62 days whereas 

the tag deployed on a large male (226 cm FL) lasted for almost 6 months. With the large amount 

of data obtained from SPOT tags, we can begin to look at large-scale patterns and whether there 

is habitat separation based on sex or size as is seen in the central Pacific. Figure 5 shows the 

tracks from male and female blue sharks. Both sexes spend considerable time in the California 

Current, with the females possibly extending farther to the north and south. When offshore, 

generally, the females move south into the subtropical convergence zone whereas the males 

make more westerly migrations. There is some suggestion in two of the longer tracks that the 

males may return to the California Current in subsequent years. Both habitat separation by sex 

and site fidelity have implications for the management of blue shark populations. For example, 
18

Figure 5. Comparison of the tracks of blue 

sharks for males (blue) and females (red) over 

the course of the study. 

fidelity to specific areas is increasingly 

recognized in fish from swordfish to 

salmon sharks (Lamma ditropis) and 

increases the potential for regional local 

depletion where fisheries exist. 

For mako sharks, 5 tags were still

transmitting in early 2012. Two of these 

were deployed in 2009, 1 was deployed 

in 2010 and the remaining 2 tags were 

deployed in 2011. The SPOT tags 

continue to be an excellent tool for 

studying the movements of mako sharks 

and the multiyear records provide an 

incredible opportunity to examine 

seasonal movement patterns and 

regional fidelity. For the two tags 

deployed in 2009, both returned for the 

third year in a row to the same 

destination. The large female (205 cm 

FL at tagging) traveled southeast of 

Hawaii and the 174 cm FL male traveled into the Sea of Cortez (Fig. 6.). Additional analyses are 

needed to determine (1) how patterns link to sex and size, (2) what triggers the onset of 

migration, and (3) what characterizes the ultimate destinations. As with blue sharks, this type of 

regional site fidelity has important implications for management.

Figure 6. Tracks from two mako sharks showing nearly three years’ worth of data and 

apparent preferences for specific regions (left 205 cm FL female, right 174 FL male). 

20

SCB and suggest biannual deposition in vertebrae. An analysis of juvenile mako shark band 

deposition patterns is now complete and a manuscript has been drafted. 

Foraging Ecology of Shortfin Mako, Blue and Common Thresher Sharks – The California 

Current is a productive eastern boundary current that is an important nursery and foraging

ground for a number of highly migratory shark species. As mentioned above, three of the most 

abundant juvenile sharks in the California Current are the shortfin mako, blue and common 

thresher sharks. To better understand niche separation and the ecological role of these 

overlapping species, stomach content analyses have been ongoing at the SWFSC since 1999. 

Stomachs are obtained primarily from the CADGN observer program. 

A synthesis comparing the foraging ecology of shortfin mako, blue and common thresher sharks

was recently published in the journal Environmental Biology of Fishes (Preti et al., 2012). In 

this study, stomach contents of sharks collected from 2002 to 2008 were identified to the lowest 

taxonomic level and analyzed using univariate and multivariate methods. Of 330 mako sharks 

sampled, 238 stomachs contained 42 prey taxa, with jumbo squid, and Pacific saury (Cololabis 

saira) representing the most important prey based on the geometric index of importance (GII). 

Of the 158 blue sharks sampled, 114 stomachs contained 38 prey taxa, with jumbo and Gonatus 

spp. squids representing the most important prey. Lastly, 225 thresher sharks were sampled and 

157 stomachs contained 18 prey taxa with northern anchovy and Pacific sardine (Sardinops 

sagax) identified as the most important prey. Overall, mako sharks had the most diverse diet, 

feeding on many species of teleosts and cephalopods, followed by blue sharks, which consumed 

a wide range of prey (primarily cephalopods), while thresher sharks were most specialized, 

feeding primarily on coastal pelagic teleosts. Despite similarities in habitat, the diets of these 

three common shark species are distinct in the California Current, indicating niche separation.

The data on shark foraging ecology were also used to develop a new approach for characterizing 

habitat use and improving our understanding of ecological interactions. We introduce a 

resampling method to indirectly estimate foraging habitat based on diet data and knowledge of 

prey habitat use. The method is unique in that (1) it is based on resampling by bootstrapping; 

and (2) it does not require quantitative prey distribution information. For this study, we 

combined diet data with qualitative prey distribution information for six different habitats 

segregated by depth and distance from shore. The combined data were organized into various 

matrices and resampled by bootstrapping to create an estimate of predator distribution based on 

prey habitat occupancy. Our method indicates a significant difference in foraging habitat. 

Generally, blue sharks foraged more frequently in offshore habitats, thresher sharks foraged 

mostly in nearshore epipelagic habitats, and makos foraged both near- and offshore in epi- and 

mesopelagic habitats. The flexibility of the new method should allow for wide application, 

adding to the suite of possible indirect techniques available to infer foraging habitat use. The 

results of this research are being prepared for publication. 

In addition to foraging ecology, we have started to investigate algal toxins (domoic acid) in 

thresher shark in the SCB. Thresher sharks forage near shore and feed on small schooling fish 

such as sardine and anchovy, making them prime candidates for exposure to domoic acid. 

Domoic acid was detected in stomach contents and blood samples collected from thresher sharks 

along the Southern California coast during September 2011. For stomach contents, 6 of 8 
21

samples were positive, with values ranging from 4.5 to 44.6 ng/g. Stomach contents of sharks 

positive for domoic acid included market squid, Pacific mackerel, and Pacific sardine – species 

well know to harbor domoic acid. Blood samples were positive in 3 of 6 cases, with values 

ranging from 0.9 to 47.9 ng/g. The value of 47.9 ng/g is one of the highest reported 

concentrations of domoic acid measured in blood from a field-collected fish or animal. These 

levels are, however, far below what would be considered toxic to humans. The regulatory limit 

for domoic acid in shellfish is 20,000 ng/g. Our findings confirm that thresher sharks are exposed 

to domoic acid, and measurable levels of this toxin can occur in their blood stream. Further 

studies are needed to document domoic acid in muscle and the potential implications of 

measured concentrations for shark and human health. 

Survival after Capture and Release – Common thresher, shortfin mako, and blue sharks are 

captured in both commercial and recreational fisheries in the California Current. The CADGN

fishery is the commercial fishery which catches the greatest number of each of these species. 

While thresher and mako sharks are landed, almost all blue sharks are discarded. For thresher 

and mako sharks, regional recreational fisheries are growing in popularity. Recreational fishers 

are often only interested in the challenge of the fight and will frequently release their catch. The 

survival rate of sharks released both from the CADGN fishery and by recreational anglers is 

unknown. Reliable estimates of removals (i.e., mortality) are necessary in order to adequately 

assess the status of the stocks and determine the effects of the fisheries on their abundance.

Blue Sharks Released from the California Drift Gillnet Fishery – The CADGN fishery targets 

swordfish in the California Current. With the exception of ocean sunfish, blue sharks are caught 

in greater numbers than any other finfish species taken in this fishery. Nearly all blue shark are 

discarded at sea due to lack of market value. A 2009 analysis of the 1990-2008 observer data 

reveals that 32% of blue sharks captured were released alive, and an additional 5% were 

discarded with their disposition unknown. The remaining 63% were discarded dead. 

In 2007, the SWFSC and the SWR began deploying PSAT tags on sharks released from the 

CADGN fishery to assess survivorship. The tags were programmed to pop off after 30 days. 

The goal was to tag sharks such that the sex ratio, range of sizes, and condition at release were 

comparable to those released from the fishery. As a part of the study, a set of criteria was 

developed to document the condition of all blue sharks released: good, fair or poor.

Since initiating the study in 2007, 12 blue sharks (100 to 200 cm FL, median 149 cm) have been 

tagged by fishery observers. Nine of these animals were male, one was female, and the sex of 2 

animals was unknown. Three of the 12 sharks were released in “good” condition while the 

remaining 9 were released in “fair” condition. Satellite tag records suggest that all animals 

survived the acute effects of capture in the CADGN fishery. Temperature, depth, and movement 

data demonstrated behavior of blue sharks that was similar to that reported in other studies. One 

tag appeared to have been ingested by a predator after 17 days and regurgitated 3 days later. 

To meet the goal of matching the general composition of the catch, additional tag deployments 

are necessary. In the fishery the sex ratio is roughly 60% male and 40% female, and from 2007 

to 2010, 29% of blue sharks were released in poor condition. Of the sharks tagged to date, none 

have been in poor condition, the average size is larger than that observed in the fishery, and few 
22

Figure 8. The SWFSC HMS lab teamed up with the Pfleger Institute 

of Environmental Research to create a best practices guide to thresher 

fishing and handling. One side of the brochure is pictured above. 

These brochures aid outreach and education efforts at industry shows 

and seminars. 

females have been tagged. Thus, tagging efforts during the 2010-2011 and 2011-2012 seasons 

were focused on smaller sharks, females, and animals released in poor condition. Tags were 

distributed among observers as widely as possible in an attempt to ensure deployment. However, 

due to the decreased effort and observer coverage, and the small numbers of blue sharks caught 

overall, particularly of the desired size, sex, and conditions, only one blue shark was tagged for 

this study during the 2011-2012 CADGN season. This shark was in fair condition and survived 

after release. The objectives for the 2012-2013 season will be to deploy more tags. Results to 

date suggest a 100% survival rate for male blue sharks released in fair or better condition. 

Thresher Sharks Released from the Recreational Fishery – The SWFSC, SWR, and Pfleger 

Institute of Environmental Research are conducting a study to assess the post-release survival of 

thresher sharks caught by recreational anglers. During the first phase of the study, sharks were 

released after tail hooking, and results demonstrated that survivorship is low for sharks greater 

than 185 cm FL or enduring fight times exceeding 85 minutes. Those results were published in 

the journal Fisheries Research in 2010 (Heberer et al., 2010). The goal of the second phase of 

the study is to determine whether sharks that are released with trailing fishing gear survive. 

Survivorship is being 

determined using PSATs

deployed on sub-adult 

and adult common 

thresher sharks. To date, 

PSATs have been 

deployed on 8 common 

thresher sharks (132 to 

175 cm FL, median 141 

cm) captured using 

fishery standard 

techniques and released 

with trailing gear. Of 

the 8 sharks, 5 died 

within 24 hours, 2

sharks survived with the 

trailing gear, and one of 

the PSATs did not 

report. The remaining

tags will be deployed

during spring 2012. 

In addition to the studies of survival, concurrent investigations on the effectiveness of degradable 

links and alternative fishing techniques to reduce tail hooking and trailing gear were also being 

performed to reduce overall post-release mortality in the recreational fishery. The results from 

all phases of this study will be used to estimate the survival rates and reduce the mortality of 

recreationally caught thresher sharks. A major component of this project is education and 

outreach to the recreational fishing community in order to promote fishing practices that enhance 

thresher shark catch and release survival (Fig. 8.).
23

Shark Stock Assessments – The SWSFC contributes to working groups of the PFMC and ISC. 

Starting in 2010, we began working with member nations of the ISC as well as scientific partners 

in Mexico and of the IATTC to conduct the first formal assessments of common thresher, blue 

and mako sharks in the North Pacific and EPO. These sharks are both fishing targets and 

incidental bycatch in numerous transboundary fisheries and their status requires long-term 

monitoring.

The first stock assessment is being conducted on thresher sharks. Thresher sharks occur along 

the coast of the U.S. and Mexico and are important to local commercial and recreational 

fisheries. While preliminary analyses suggest that the population is rebounding after declines in 

the early 1980s, no official stock assessment has been conducted and analyses to date have only 

included data from the U.S. A stock assessment will better reflect population level trends if data

from the entire range are included. Preliminary analyses confirm previous indications that the 

stock biomass is increasing.

Basking Shark Research Program – The eastern North Pacific basking shark population 

appears to have declined dramatically in the last 50 years with no evidence of recovery. Where 

hundreds to thousands of individuals were observed off the U.S. West Coast in the early to mid1900s, sighting even a few individuals is now rare. The apparent reduced abundance in the 

eastern North Pacific is likely linked to targeted fisheries off California in the first half of the 

1900s and the eradication program established off Canada to keep basking sharks from 

destroying salmon nets. Due to concern about basking shark populations along the west coast of 

North America, the basking shark was listed as endangered in Canada and as a Species of 

Concern in the U.S. in 2010. Unfortunately, efforts to understand trends are hampered by the 

lack of basic data on movements, the influence of environment on abundance and distribution, 

information on the full geographic range of the eastern North Pacific stock, and basic life-history 

information. Given the severe data gaps for this population, the SWFSC initiated a basking 

shark research program in 2010 with SOC funding to (1) mine existing data for additional 

biological information, (2) conduct an electronic tagging study, (3) improve international data 

collection, and (4) improve national sightings information by developing a sightings website and 

an education and outreach program centered around Monterey Bay, California. Monterey is a 

historic basking shark hotspot where the California basking shark fishery in the early 1900s was 

based. 

This research program has progressed at a number of different levels. A dedicated website

(http://swfsc.noaa.gov/baskingshark/), email (basking.shark@noaa.gov), and hotline (858-334-

2884) have been established as a part of a sightings network. Information on sightings will help 

with documenting patterns of occurrence and tagging efforts. We also developed a trinational 

team with colleagues in Canada and Mexico to coordinate research efforts. The second meeting 

of the trinational team took place in May 2011. In addition, we deployed two satellite tags on

basking sharks off San Diego in the summer of 2011. 

The use of satellite tags is critical for examining large-scale movement patterns and habitat use, 

which are essential for understanding patterns and trends in abundance. The first tag deployed in 

2011 released early after 8 days and floated to a beach where the tag was recovered. No track 

was estimated for this tag given the short deployment duration. The second tag remained on the 

25

master’s thesis completed in collaboration with the University of San Diego and SWFSC 

provided evidence of regional stock structure within the Pacific. Her study, using mitochondrial 

haplotype data, showed a strong subdivision between northern and southern hemisphere 

populations, with additional subdivision between southeast and southwest Pacific populations; 

however, no subdivision was found in the North Pacific using this marker. The results of this 

study have been updated with additional samples collected in the western Pacific and are being 

prepared for publication. As part of his Ph.D. work at University of California Davis and San 

Diego State University in collaboration with the SWFSC, Dovi Kacev has been developing a 

suite of nuclear microsatellite markers to further refine the spatial and temporal resolution of 

shortfin mako stocks within the Pacific. In addition to studies of stock structure, these markers 

will be used to develop estimates of effective population size within the California Current 

region. Currently data generation and analyses are underway for the Pacific studies. These 

markers have also been shared with international collaborators and are currently being applied to 

global studies of shortfin makos. 

Common Thresher Shark – Common threshers are commonly encountered in temperate coastal 

marine fisheries but little is known about regional connectivity. In recent years they have 

become part of an increasingly important recreational fishery in Southern California in addition 

to being an important component of local gillnet fisheries. In order to better understand 

population connectivity, Dovi Kacev has been developing nuclear microsatellite markers for this 

species as well. Application of these markers has begun and data collection is just beginning.

Opah – The opah or moonfish is found worldwide in tropical and subtropical waters. Though 

caught mainly as bycatch in pelagic tuna fisheries, opah command a high price in the market and 

thus few are discarded. Despite being known to science for over 230 years, the existence of two 

morphotypes in the North Pacific was only recently discovered by PIFSC port samplers in 

Honolulu. The most conspicuous difference between these morphotypes is the relative size of 

the eye, leading to the labeling of the morphotypes as “big-eye” and “small-eye” opah. Genetic 

analyses performed at the SWFSC confirm that the two morphotypes are genetically distinct and 

in fact represent separate species. In an effort to understand the distribution of these two species, 

additional samples have been acquired from museums and observer programs worldwide. 

Examination of these samples has provided evidence for additional cryptic species and suggests 

there are at least five species within the opah species complex. Genetic analyses, species 

descriptions, and distribution maps are being prepared for publication.

Outreach – In an effort to increase international collaboration and capacity building, a genetic 

species identification course was taught at the III Taller Interregional de Tiburones en el Océano 

Pacífico Oriental in Manta, Ecuador, 6-9 July 2010. This course involved hands-on experience 

using locally collected shark fins. The goals were to both genetically identify species groups that 

are commonly misidentified such as the hammerhead and thresher sharks, as well as species 

common in this region. Some of the techniques are now being applied to studies of shark 

landings in Columbia and the initial results and methods have been published in the journal

Molecular Ecology Resources (Caballero et al., 2012).

VI. IDCPA RESEARCH

The SWFSC research conducted under the International Dolphin Conservation Program Act 
26

(IDCPA) during 2011 was focused on evaluating line transect methodology and the potential 

roles of the fishery and ecosystem in the apparent lack of recovery of depleted dolphin stocks in 

the eastern tropical Pacific Ocean (ETP). This lack of recovery follows a period of significant 

reductions in observed dolphin mortality in the ETP tuna purse seine fishery. Research activities 

included (1) analysis of data collected during the 2007 survey designed to collect fine-scale 

ecosystem data and assess standard methods for collecting dolphin sighting data, and (2) other 

data analyses, processing, and publications. 

Analysis of Stenella Abundance Research-Line Transect and Ecosystem Survey Data – In 

2007, SWFSC conducted a Stenella Abundance Research-Line Transect and Ecosystem (STARLITE) cruise to survey marine mammals and their habitat in the ETP. The primary objective of 

the STAR-LITE cruise was to investigate line transect methods used on surveys in the ETP and 

to explore fine-scale spatial and temporal variability in the ecosystem using a multidisciplinary 

approach. 

Two different cetacean survey methodologies (“passing mode” and “closing mode”) were 

compared using both empirical data and simulation models, and a manuscript has been published 

in the Journal of Cetacean Research and Management (Schwarz et al., 2010). Passing survey 

mode—when the survey ship does not make any changes in course to approach a cetacean 

sighting—was compared with closing survey mode—when such course changes are made to 

further investigate the sighting. The results of the analysis indicated that observers are able to 

identify animals to species less often and that estimates of dolphin group size are lower when 

surveys are conducted in passing mode (no course changes are made). However, conducting 

surveys in closing mode results in lower encounter rates due to the stop-start nature of the survey 

method. Continuing to explore potential sources of bias in our methods and explicitly 

accounting for these in our models is critical to refining our models and ultimately improving our 

approaches to estimating abundance of ETP dolphins and other cetaceans.

Ecosystem data collected on this same cruise (STAR-LITE 2007) have been analyzed. As 

expected, environmental variability within days and day-to-day was relatively small. However, 

the passage of tropical storm Kiko through the study area caused persistent changes in the entire 

ecosystem. Wind mixing decreased surface temperature and reduced fine-scale variability. The 

thermocline shoaled and stratification decreased. Chlorophyll in the surface layer increased, 

apparently due to both mixing of phytoplankton from depth and to enhanced production. 

Macrozooplankton biomass increased slowly, perhaps in response to the increased phytoplankton 

production. These environmental changes had a variety of effects on mid-trophic and apex 

predator components of the ecosystem. Changes in flying fish abundance and diet, and in the 

abundance and community composition of both seabirds and cetaceans are being investigated. A 

paper describing these results is in preparation.

This is the eleventh year of similar investigations conducted during the past 20 years, with 

previous cruises in 1986-1990, 1998-2000, 2003, and 2006. Using an ecosystem approach, we 

conducted research on physical and biological oceanography (dolphin habitat); midtrophic-level 

fishes and squids (dolphin prey); and seabirds, marine turtles, and other cetaceans (dolphin 

commensals, competitors, and predators). Data and analyses resulting from STAR surveys form 

the basis for many international measures adopted to conserve dolphin stocks and manage the 
27

tuna purse seine fishery in the ETP. The next full STAR survey, scheduled to occur in the fall of 

2009, was postponed by one year due to ship time constraints. On 6 April 2010, STAR 2010 

was again postponed due to the same constraints. And in January 2010, plans for conducting 

STAR in the fall of 2011 were canceled indefinitely. At this time, the future of these cetacean 

and ecosystem assessment cruises is uncertain. 

Data Analyses, Processing, and Publication – The SWFSC’s investigations of dolphin stocks 

historically depleted by the ETP tuna purse seine fishery (spinner, Stenella longirostris, and 

pantropical spotted, S. attenuata, dolphins) are conducted with an ecosystem approach. In 

addition to investigating the status and trends of these dolphin stocks, auxiliary projects are 

conducted to improve our understanding of their surrounding environment. Data analyses, 

processing, and publications included (1) investigations of cetacean biodiversity hotspots; (2) 

identifying critical habitat for large whales; (3) ecosystem modeling; (4) assessment of relative 

fishery exposure for ETP dolphins; (5) variation and predictors of vessel response behaviors in 

ETP dolphins; (6) dolphin swimming kinematics research; (7) investigations of dolphin 

reproductive biology; (8) ETP dolphin population genetic structure; (9) investigations of the ETP 

ecosystem and its change over time; (10) metrics of ecosystem impact of the ETP purse seine 

fishery; and (11) cephalopods as indicators of spatial variation in biochemical properties between 

marine systems.

Investigations of Cetacean Biodiversity Hotspots – A paper was published (Kaschner et al.,

2011) with Gerrodette as a co-author. This paper uses a model to predict cetacean species 

richness patterns, and validates the model with empirical data, including data collected in the 

ETP. 

Ballance, Redfern, and Pitman are finalizing a manuscript investigating species richness hotspots 

for 28 species of cetaceans in the ETP (ca. 20 million km2

) based on data collected using line 

transect methods aboard NOAA research vessels, August–November, in each of 10 years during 

a 21-year period (1986-2006). Density was calculated using species- and area-specific published 

values of g(0) and f(0), and interpolated throughout a 1° x 1° grid of the study area using two 

smoothing algorithms and two resolutions. Density was converted to presence/absence on a 

species-specific basis, and species richness (number of species recorded in a particular grid cell) 

was mapped for all years combined. Richness hotspots were defined as any grid cell that 

contained greater than 40% of the total species pool (≥ 11 species) and were clearly evident in 

three distinct regions: the Equatorial Front, the Costa Rica Dome, and waters to the southwest of 

the Baja California peninsula. Although these hotspots encompassed areas of highest density for 

a few species, the correlation between richness and density for any given species was generally 

low (mean 0.25, range 0.03 to 0.44), as was the proportion of cells where a particular species was 

present and encompassed by a hotspot (mean 20%, range 4% to 56%). These results were robust 

to smoothing algorithm and spatial resolution. 

Identifying Critical Habitat for Large Whales – Many species of baleen whales migrate long 

distances between breeding and feeding areas. These species are exposed to anthropogenic 

threats in their feeding and breeding areas and along their migration routes; threats include 

entanglement in fishing gear, ship strikes, ocean noise, contaminants, and climate change. 

Mitigating these threats requires a transboundary, systematic planning approach. We are using 
28

three species of baleen whales in the ETP to explore several components of the planning process. 

The ETP is seasonally occupied by migratory blue and humpback whales from both northern and 

southern hemispheres; it also hosts important numbers of resident Bryde’s whales. We will use 

10 years of large-scale survey effort in offshore waters to compare two methods for predicting 

species density: habitat models (using sea surface temperature, salinity, and chlorophyll, mixed 

layer depth, and sea floor depth as predictor variables) and inverse distance weighted

interpolation of daily density estimates. Generalized additive models will be used to relate 

habitat variables to an effort-corrected estimate of the number of whales. Both methods will be 

used to derive a synoptic grid of density for blue, humpback, and Bryde’s whales. For 

humpback whales, we will also predict the location of breeding areas using an envelope model of 

mother-calf sightings in coastal surveys off Mexico, Costa Rica, Panama, and Ecuador. 

Different metrics for delineating critical habitat (e.g., protecting a percentage of a population, 

protecting areas of known occurrence, or protecting known breeding or feeding areas) will be 

applied to the density grids for each species. 

Ecosystem Modeling – Development of an ecosystem model to explore patterns of cetacean 

distribution, migration, feeding, and breeding has begun. Data fields used by Patrick Lehody 

(France) to drive a spatial ecosystem and population dynamics model (SEAPODYM) for tuna 

were obtained (temperature, salinity, currents, chlorophyll, primary productivity, and mid-trophic 

level biomass). Comparisons of SEAPODYM model data to data collected on SWFSC cetacean 

and ecosystem assessment surveys have been completed for the California Current and will be 

done for the ETP. The next step is to test whether the inclusion of mid-trophic level biomass 

improves cetacean habitat models. In the future, we will use these ecosystem variables to drive a 

population- or individual-based model of cetacean species to explain current ecological patterns 

and predict future changes.

Assessment of Relative Fishery Exposure for ETP Dolphins – For the past half century, the 

purse seine fishery for yellowfin tuna has been a significant factor in the lives of dolphins in the 

ETP. However, little is known about how frequently an individual dolphin is exposed to the 

fishery, and no methods are available for accurately assessing the prior exposure of dolphins

encountered at sea. Archer et al. (2010) developed a method to estimate an index of exposure 

based on a model of dolphin movement derived from data collected from multiple tracking 

studies. Based on this movement model, the method weights purse seine sets given their 

distance from a particular school of dolphins sighted at sea and how long ago they occurred. The 

method also takes into account the species composition and school size in the set. In their paper, 

as a demonstration, the authors use the method to examine the spatial and temporal distribution 

of this index over an 11-year period for which we have detailed data on purse seine sets. While 

the method was designed for examining exposure to the ETP purse seine fishery, it is also 

applicable to studies of other anthropogenic effects where there is concern about exposure rates, 

such as underwater sound, pollution, or ship strikes. Planned studies for this index include 

examining its relationship to evasive behavior, calf production as assessed from aerial 

photographs, and reproductive rates as measured from skin biopsies.

Variation and Predictors of Vessel Response Behaviors in ETP Dolphins – Dolphins exhibit a 

range of vessel response behaviors, from those that readily approach and bow ride to others that 

are indifferent or actively evasive. However, the factors responsible for this variation have not 
29

been examined. Archer et al. (2010) used a tree-based modeling method to investigate the 

influence of geography, time of day, species composition, and fishery exposure on the responses 

of five species of dolphins in the ETP, comprising 10 management stocks. Data were collected 

for 2,667 sightings during four research cruises between 1998 and 2003. The relative frequency 

of five responses (approaching the vessel, bow riding, running, school splitting, and low 

swimming) showed significant (p < 0.0005) variability among species, as well as stocks within 

the same species. Striped (Stenella coeruleoalba), whitebelly spinner (S. longirostris), and 

western-southern pantropical spotted dolphins (S. attenuata attenuata) tended to be evasive, 

while coastal spotted (S. attenuata graffmani) and common bottlenose dolphins (Tursiops 

truncatus) tended to be attracted to the vessel. There was a strong tendency of dolphins sighted 

offshore to be significantly more evasive than those less than about 100 nmi from the coast. The 

degree of evasiveness in stocks that are frequently targeted by the tuna purse seine fishery 

(northeastern spotted, S. attenuata; eastern spinner, S. longirostris orientalis; and short-beaked 

common, Delphinus delphis) was greater with more purse seine activity in the vicinity, while no 

significant relationship was found for those stocks that are rarely set on. For each stock, vessel 

response had a relatively unique suite of predictors, indicating an interplay of intrinsic, natural 

extrinsic and anthropogenic factors.

Dolphin Swimming Kinematics Research – In September 2011, the final paper was published in 

the series of studies investigating swimming kinematics of mother and calf dolphins. These 

studies are part of an effort to determine whether chase and encirclement of dolphin mother-calf 

pairs by tuna purse seiners in the ETP may be contributing to lack of population recovery. This 

paper (Noren et al., 2011) presents the first empirical analysis of the hydrodynamic effects of late 

pregnancy on swimming kinematics of female dolphins. Study results show that morphological 

changes during late pregnancy, particularly the large increase in frontal cross section as well as 

the decreased amplitude of propulsive movements by the flukes, lead to significant decreases in 

swim performance during this period. Results from this series of studies will contribute to 

development of a hydrodynamics-based energetics model investigating the potential for dolphin 

mother-calf separation and subsequent calf mortality due to tuna purse seine chase in the ETP.

Investigations of Dolphin Reproductive Biology – A doctoral dissertation (Kellar et al., 2008) 

was completed examining the pregnancy patterns of spotted dolphins in the ETP. This work has 

been revised and submitted to Marine Ecology Progress Series for review. It states that one 

hypothesis for the lack of recovery of the spotted dolphin population in the ETP is that continued 

chase and encirclement by the tuna fishery negatively affects reproduction. 

Insufficient life history sampling in this region over the last decade makes traditional estimation 

of population reproductive rates impossible. The current reproductive patterns of these dolphins 

were examined using a molecular method to assess pregnancy state from blubber progesterone 

concentrations in biopsy samples. Blubber progesterone was quantified in 212 biopsies from 

female offshore spotted dolphins sampled between 1998 and 2003 in the northeastern tropical 

Pacific. These concentrations were found to be sharply bimodal with no value observed between 

49 ng/g and 87 ng/g, a finding consistent with the concentration gap between known pregnant 

and non-pregnant dolphins. Given that high blubber progesterone (≥ 87 ng/g) indicates 

pregnancy, we found that 11.8% of the biopsied females were pregnant. This is substantially 

lower than an estimate of the proportion pregnant found in the fishery kill over the same region
30

(22.3%) between 1973 and 1992. To try to ascertain the potential cause of this discrepancy, the 

relationship between pregnancy and fishery exposure was analyzed, and we found that pregnant 

females were exposed to significantly less fishery activity than non-pregnant ones (P < 0.046), 

suggesting that the fishery has an inhibitive effect on pregnancy. However, there are several 

caveats to this finding, and how this relationship might explain the discrepancy between these 

data sets is unclear. We also examined and modeled spatial patterns of reproduction and found 

that pregnancy was more aggregated than random (P = 0.020), with the highest proportion 

pregnant in the mouth of the Gulf of California, an area with relatively low reported fishery 

activity. 

In 2009, work began quantifying the levels of progesterone in spinner dolphins to replicate this 

study in another fishery-impacted species. To date, 189 animals have been processed; hormones 

have been measured and pregnancy determination is complete. The next step is to analyze and 

add a spinner dolphin-specific fishery exposure index to these data and assess the relationship 

between reproduction and exposure.

ETP Dolphin Population Genetic Structure – Research is underway to determine population 

genetic structure for spotted and spinner dolphins in the ETP. Cranial and external morphology, 

as well as reproductive strategies, differ across the range of these animals; thus, genetic 

differences are expected. Population structure information is needed to develop accurate stock 

abundance estimates for population-specific dolphin bycatch limits.

In 2011, work began quantifying the levels of genetic structure in spinner and spotted dolphin 

populations in the ETP. Matthew Leslie (Ph.D. student at Scripps Institution of Oceanography) 

has collected DNA sequence data for a subset of biopsy samples (n=250) using high-throughput 

DNA sequencing. These data include 80 nuclear loci (84Kbp) and entire mitochondrial genomes 

(16Kbp). The mitogenomic data are currently being analyzed using an integrated phylogenetic 

and population genetic framework to characterize variability and structure. Additional samples 

are being sequenced from throughout the spinner dolphin distribution in order to place these 

populations within a global phylogeographic context. Nuclear DNA data have been used to 

develop single nucleotide polymorphism (SNP) assays that will be employed in genotyping 

additional modern and historical specimens.

The next step is to analyze the mitogenomic data and collect additional nuclear SNP genotypes 

using the assays developed. Additional sampling of museum specimens may be required.

Investigations of the ETP Ecosystem and Its Change over Time – An analysis of variations in 

thermocline depth and stratification in the eastern tropical and North Pacific has been accepted 

for publication, pending revision, in the Journal of Climate (Fiedler et al., 2012). Time series 

from 1958-2008 were decomposed into seasonal, interannual cycle, and long-term trend 

components using state-space techniques. On shorter time scales, interannual variations related 

to the El Niño-Southern Oscillation (ENSO) are seen. Long-term regional variability is 

observed, either a monotonic trend or with one or more change points resembling climate regime 

shifts. Such changes in upper-ocean structure and associated ecosystem effects are well known 

in well-monitored regions such as the California Current. In the eastern equatorial Pacific, the 

pycnocline has shoaled but become less stratified, while in the ETP warm pool, pycnocline depth 
31

and stratification has varied up and down with little overall change. The thermocline influences 

nutrient input to surface waters, which limits primary productivity throughout this region. 

Potential ecosystem effects of the observed long-term trends are discussed. Further analysis will 

quantify the extent to which interannual cyclic variability observed at higher latitudes, for 

example in the California Current, is related to ENSO.

Vilchis and Ballance completed a retrospective study analyzing trophic level of seabirds in the 

eastern Pacific warm pool during the past 50 years. They set out to gauge effects of the 1976-77 

regime shift of the Pacific Ocean in a tropical and pelagic community of seabirds. Using study 

skins of historical specimens from museum collections, they retrospectively (1960-2006) 

measured stable carbon (δ13C) and nitrogen (δ15N) isotopes for a suite of ecologically and 

phyolgenetically diverse seabirds from the eastern Pacific warm pool. In this region, seabirds 

generally forage by depending on subsurface predators to drive prey to the surface or by 

associating with oceanographic features that increase productivity or aggregate prey in space or 

time. They did not find community-wide changes in response to the 1976-77 regime shift.

Instead, they found evidence suggesting a trophic shift and or change in foraging area for sooty 

terns (Onychoprion fuscatus) and a long-term decrease in feather δ13C for the eastern Pacific 

warm pool seabird community. This long-term decrease in feather δ13C can be accounted for by 

the Suess effect and not a decline in primary productivity of the system. Vilchis and Ballance

hypothesize that a deepening trend in thermocline depth in the eastern Pacific warm pool is 

affecting sooty terns more so than other species in the subsurface predator-dependent guild 

which depend less on smaller subsurface predators like skipjack tuna. The manuscript of this 

study is currently in revision.

Metrics of Ecosystem Impact of the ETP Purse Seine Fishery – A manuscript was recently 

published (Gerrodette et al., 2012) that summarizes the ecological effects of the ETP purse seine 

tuna fishery by measuring the total removals (target catch and bycatch) using a variety of 

metrics. It was found that floating-object sets removed 2-3 times as much biomass per set as 

dolphin or unassociated sets. However, the three types of purse seine fishing differed in the 

composition and amount of both target catch and bycatch. Metrics of ecosystem removal which 

measured diversity, trophic level, and replacement time were more informative than metrics of 

biomass or numbers of individuals.

Cephalopods as Indicators of Spatial Variation in Biochemical Properties between Marine 

Systems – Ruiz-Cooley et al. (2010) and Ruiz-Cooley and Gerrodette (in review) quantified two 

biochemical tracers (δ13C and δ15N) from epi-mesopelagic squid tissues, the jumbo squid and 

purple back squid (Stenotheuthis oualaniensis), to investigate ontogenetic shifts in diet, habitat 

use and differentiate distinct groups or subpopulations based on the unique biochemical 

properties of their habitat along the eastern Pacific. These two squid species are key components

in food webs from the ETP and potential prey of tuna and dolphins as well as other pelagic fish 

and odontocetes. For the first time, Ruiz-Cooley and Gerrodette revealed that δ13C and δ15N 

measured from tissues of these squid species can serve to track large-scale latitudinal, 

longitudinal, and geographic variability in the biochemical distribution of carbon and nitrogen 

along the eastern Pacific. Furthermore, the results from this study can serve for future studies 

using stable isotope analysis investigating pelagic food web dynamics, which are not well 

known. 
32

Challenge against the U.S. Dolphin-Safe Labeling Standard for Tuna – In October 2008, 

Mexico filed a request for World Trade Organization (WTO) dispute settlement consultations 

with the United States. Mexico made several claims that U.S. dolphin-safe measures are 

inconsistent with various aspects of the Agreement on Technical Barrier to Trade and the 

General Agreement on Tariffs and Trade. Specifically, Mexico argued the U.S. measures:

• create a competitive disadvantage for Mexican tuna products;

• are more trade restrictive than necessary to achieve their objectives – specifically, to 

inform consumers and ensure the U.S. market is not used to encourage fishing practices 

that adversely affect dolphins; and

• could be replaced by a less trade restrictive alternative labeling standard that allows tuna 

that is caught by chasing and encircling dolphins to be labeled as dolphin-safe as long as 

no dolphins are observed killed or seriously injured, and that still meets the U.S.

objectives.

In support of these arguments, Mexico claimed that (1) ETP dolphin stocks are recovering, (2) 

there is no evidence that the fishery in impacting dolphins beyond observed kills, (3) there is an 

inconsistency between the standards that apply to tuna inside and outside the ETP, assuming that 

dolphin bycatch and intentional chase and encirclement of dolphins occurs in tuna fisheries 

outside the ETP, (4) catching tuna in association with dolphins is better for tuna stocks and the 

ecosystem because it results in primarily mature yellowfin with less bycatch of non-target 

species than other tuna fishing methods, and (5) U.S. consumers are actually unclear on the 

current dolphin-safe definition, so the U.S. measures fail to meet the objective of not misleading 

tuna consumers. 

In briefs and oral arguments the United States cited the fundamental difference in tuna-dolphin 

associations inside and outside the ETP as a basis for its labeling scheme and relied heavily on 

results from its IDCPA research program and decades of prior SWFSC research and monitoring 

in the ETP to refute Mexico’s claims. Specifically, the United States cited several published 

papers that indicate when using ecologically meaningful metrics fishing on dolphins is not 

obviously better than other methods of catching tuna and that indicate ETP dolphin stocks are 

not increasing at a rate consistent with recovery and that there is substantial evidence to support 

the hypothesis that unobserved impacts of intentional chase and encirclement (e.g., mother-calf 

separation and lower calf production in areas of greater purse seine fishing effort) are impeding 

recovery.

A panel was established to consider Mexico’s claims. A panel report was made public on 15 

September 2011, rejecting most of Mexico’s claims. The panel found that the objectives of the 

U.S. measures are legitimate, that the measures do not treat Mexico’s tuna products any less 

favorably than tuna products from the United States or other WTO members, and that any 

adverse effects felt by Mexican tuna producers from the U.S. labeling requirements are the result 

of choices made by Mexico’s own fishing fleet and canners. However, the panel also found the 

U.S. measures to be more trade restrictive than necessary to achieve the objectives of the 

measures. 

Following issuance of the panel’s report, both Mexico and the United States appealed the WTO 
33

panel’s findings to a WTO Appellate Body. Decisions on those appeals are expected in 2012.

VII. PUBLICATIONS

Literature Cited

Archer, F., J. Redfern, T. Gerrodette, S. Chivers, and W. Perrin. 2010. Estimation of relative 

exposure of dolphins to fishery activity. Mar. Ecol. Prog. Ser. 410:245–255.

Benson, S., H. Dewar, P. Dutton, C. Fahy, C. Heberer, D. Squires, and S. Stohs. 2009. 

Swordfish and Leatherback Use of Temperate Habitat (SLUTH): Workshop Report. H. 

Dewar (ed.). Southwest Fish. Sci. Cent. Admin. Rep., La Jolla, LJ-09-06, 35 p.

Caballero, S., D. Cardeñosa, G. Soler, and J. Hyde. 2012. Application of multiplex PCR 

approaches for shark molecular identification: feasibility and applications for fisheries 

management and conservation in the Eastern Tropical Pacific. Mol. Ecol. Res. 12:233–

237.

Childers, J., S. Snyder, and S. Kohin. 2011. Migration and behavior of juvenile North Pacific 

albacore (Thunnus alalunga). Fish. Oceanogr. 20:157–173.

Fiedler, P. C., R. Mendelssohn, D. M. Palacios, and S. J. Bograd. (Accepted). Pycnocline 

variations in the eastern tropical and North Pacific, 1958–2008. J. Climate.

Gerrodette, T., R. Olson, S. Reilly, G. Watters, and W. Perrin. 2012. Ecological metrics of 

biomass removed by three methods of purse-seine fishing for tunas in the eastern tropical 

Pacific Ocean. Conserv. Biol. 26:248–256.

Heberer, C., S. A. Aalbers, D. Bernal, S. Kohin, B. DiFiore, and C. A. Sepulveda. 2010.

Insights into catch-and-release survivorship and stress-induced blood biochemistry of 

common thresher sharks (Alopias vulpinus) captured in the southern California 

recreational fishery. Fish. Res. 106:495–500.

Kaschner, K., D. Tittensor, J. Ready, T. Gerrodette, and B. Worm. 2011. Current and future 

patterns of global marine mammal biodiversity. PLoS ONE 6(5):e19653.

Kellar, N. M., M. L. Trego, S. J. Chivers, and F. I. Archer. 2008. Pregnancy patterns of spotted 

dolphins in the eastern tropical Pacific determined from hormonal analysis of biopsies and 

their correlation with the purse-seine tuna fishery. Ph.D. thesis, Univ. of Calif. San Diego, 

La Jolla, Calif., 186 p. 

Noren, S. R., J. V. Redfern, and E. F. Edwards. 2011. Pregnancy is a drag: hydrodynamics, 

kinematics and performance in pre- and post-parturition bottlenose dolphins (Tursiops 

truncatus). J. Exp. Biol. 214:4151–4159.

Preti, A., C. U. Soykan, H. Dewar, R. J. D. Wells, N. Spear, and S. Kohin. (In press). 

Comparative feeding ecology of shortfin mako, blue and common thresher sharks in the 

California Current. Environ. Biol. Fish. doi: 10.1111/j.1755-0998.2012.03149.x.

Ruiz-Cooley, R. I., E. C. Villa, and W. R. Gould. 2010. Ontogenetic variation of δ13C and δ15N 

recorded in the gladius of the jumbo squid Dosidicus gigas: geographic differences. Mar.

Ecol. Prog. Ser. 399:187–198.
34

Schwarz, L. K., T. Gerrodette, and F. I. Archer. 2010. Comparison of closing and passing mode 

from a line-transect survey of delphinids in the eastern tropical Pacific Ocean. J. 

Cetacean Res. Manag. 11:253–265.

Wells, R. J. D., S. Kohin, S. L. H. Teo, O. E. Snodgrass, and K. Uosaki. 2011. Age and growth 

of North Pacific albacore (Thunnus alalunga). Working paper ISC/11/ALBWG/02 

submitted for the ISC Albacore Working Group Meeting, June 2011. Shimizu, Japan.

Yabuta, Y., and M. Yukinawa. 1963. Growth and age of albacore. Rep. Nankai Reg. Fish. Res. 

Lab. 17:111–120.

Published

Abecassis, M., H. Dewar, J. Polovina, and D. Hawn. (In press). Modeling swordfish daytime 

vertical habitat in the North Pacific Ocean from pop-up archival tags. Mar. Ecol. Prog. 

Ser. 

Block, B. A., I. D. Jonsen, S. J. Jorgensen, A. J. Winship, S.A. Shaffer, S. J. Bograd, E. L. 

Hazen, D. G. Foley, G. A. Breed, A-L. Harrison, J. E. Ganong, A. Swithenbank, M. 

Castleton, H. Dewar, B. R. Mate, G. L. Shillinger, K. M. Schaefer, S. R. Benson, R. W. 

Henry, and D. P. Costa. Tracking apex marine predator movements in a dynamic ocean. 

Nature 475:86–90. 

Caballero, S., D. Cardeñosa, G. Soler, and J. Hyde. 2012. Application of multiplex PCR 

approaches for shark molecular identification: feasibility and applications for fisheries 

management and conservation in the Eastern Tropical Pacific. Mol. Ecol. Res. 12:233–

237.

Childers, J., S. Snyder, and S. Kohin. 2011. Migration and behavior of juvenile North Pacific 

albacore (Thunnus alalunga). Fish. Oceanogr. 20:157–173.

Dewar, H., E. Prince, M. K. Musyl, R. W. Brill, C. Sepulveda, J. Lou, D. Foley, E. S. Orbesen, 

M. L. Domeier, N. Nasby-Lucas, D. Snodgrass, R. M. Laurs, B. A. Block and L. A. 

McNaughton. 2011. Movements and behaviors of swordfish in the Atlantic and Pacific 

oceans examined using pop-up satellite tags. Fish. Oceanogr. 20:219–231.

Gerrodette, T., R. Olson, S. Reilly, G. Watters, and W. Perrin. 2012. Ecological metrics of 

biomass removed by three methods of purse-seine fishing for tunas in the eastern tropical 

Pacific Ocean. Conserv. Biol. 26:248–256.

Hoolihan, J. P., J. Luo, F. J. Abascal, S. E. Campana, G. De Metrio, H. Dewar, M. L. Domeier, 

L. A. Howey, M. E. Lutcavage, M. K. Musyl, J. D. Neilson, E. S. Orbesen, E. D. Prince,

and J. R. Rooker. 2011. Evaluating irregular post-release behaviour of large pelagic 

fishes deployed with pop-up satellite archival tags. ICES J. Mar. Sci. 68:880–889.

Kaschner, K., D. Tittensor, J. Ready, T. Gerrodette, and B. Worm. 2011. Current and future 

patterns of global marine mammal biodiversity. PLoS ONE 6(5):e19653.

Noren, S. R., J. V. Redfern, and E. F. Edwards. 2011. Pregnancy is a drag: hydrodynamics, 

kinematics and performance in pre- and post-parturition bottlenose dolphins (Tursiops 

truncatus). J. Exp. Biol. 214:4151–4159.
35

Perrin, W. F., and S. J. Chivers. 2011. Osteological specimens of tropical dolphins (Delphinus, 

Grampus, Lagenodelphis, Stenella, Steno and Tursiops) killed in the tuna fishery in the 

eastern tropical Pacific (1966-1992) and placed in museums by the Southwest Fisheries 

Science Center. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-SWFSC-477, 89 p. 

Preti, A., C. U. Soykan, H. Dewar, R. J. D. Wells, N. Spear, and S. Kohin. (In press).

Comparative feeding ecology of shortfin mako, blue and common thresher sharks in the 

California Current. Environ. Biol. Fish.

Ruiz-Cooley, R. I., E. C. Villa, and W. R. Gould. 2010. Ontogenetic variation of δ13C and δ15N 

recorded in the gladius of the jumbo squid Dosidicus gigas: geographic differences. Mar.

Ecol. Prog. Ser. 399:187–198.

St. Aubin, D. J., K. A. Forney, S. J. Chivers, M. D. Scott, K. Danil, and T. A. Romano. In press.

Hematological, serum, and plasma chemical constituents in pantropical spotted dolphins 

(Stenella attenuata) following chase, encirclement, and tagging. Mar. Mamm. Sci. doi: 

10.1111/j.1748-7692.2011.00536.x.

Teo, S. L. H., P. T. Sandstrom, E. D. Chapman, R. Null, K. Brown, A. P. Klimley and B. A. 

Block. 2011. Archival and acoustic tags reveal the post-spawning migrations, diving 

behaviour, and thermal habitat of hatchery-origin Sacramento River steelhead kelts 

(Onchorhynchus mykiss). Environ. Biol. Fish. doi:10.1007/s10641-011-9938-4.

Weng, K., J. O’Sullivan, C. Lowe, C. Winkler, M. Blasius, K. Loke-Smith, T. Sippel, J. Ezcurra, 

S. Jorgensen, and M. Murray. 2012. Back to the wild: Release of juvenile great white 

sharks from the Monterey Bay Aquarium. In M. L. Domeier (ed.), Global Perspectives 

on the Biology and Life History of the Great White Shark, p. 419–446. CRC Press.

Technical Reports, Administrative Reports, and Working Papers

Albacore Working Group of the ISC. 2011. Stock assessment of albacore tuna in the North 

Pacific Ocean in 2011. Report of the ISC Albacore Working Group Meeting, 30 May–11 

June 2011. Shimizu, Japan.

Kohin, S., and J. Wraith. 2011. The 2010 Billfish Newsletter. Southwest Fish. Sci. Cent., La 

Jolla, Calif. 

MacCall, A. D., and S. L. H. Teo. 2011. Exploration of a hybrid Stock Synthesis-VPA model of 

Pacific bluefin tuna to distinguish between trends in recruitment and changes in fishing 

intensity on young fish. ISC/11-1/PBFWG/01. Working document submitted to the ISC 

Pacific Bluefin Tuna Working Group Meeting, 6-13 January 2011. Shimizu, Japan.

Michaud A., J. Hyde, S. Kohin, and R. Vetter. 2011. Mitochondrial DNA sequence data reveals 

barriers to dispersal in the highly migratory shortfin mako shark (Isurus oxyrinchus). 

Working paper ISC/11/SHARKWG-2/03 submitted for the ISC Shark Working Group 

Meeting, 28 November–3 December 2011. La Jolla, Calif., USA.

Piner, K., H. H. Lee, I. Taylor, A. Aires-da-Silva, and S. L. H. Teo. 2011. Introduction of a 

spatially structured model of Pacific bluefin tuna. ISC/11-1/PBFWG/06. Working 
36

document submitted to the ISC Pacific Bluefin Tuna Working Group Meeting, 6-13 

January 2011. Shimizu, Japan.

Sippel, T., J. Wraith, S. Kohin, J. Holdsworth, V. Taylor, M. Taguchi, H. Matsunaga, and K. 

Yokawa. 2011. A summary of blue shark (Prionace glauca) and shortfin mako shark 

(Isurus oxyrinchus) tagging data available from the Pacific Ocean. Working document 

ISC/11/SHARKWG-2/04 submitted for the ISC Shark Working Group Meeting, 28 

November–3 December 2011. La Jolla, Calif., USA.

Southwest Fisheries Science Center. 2011. Director's report to the 62nd Tuna Conference on 

tuna and tuna-related activities of the Southwest Fisheries Science Center. Southwest 

Fish. Sci. Cent. Admin. Rep., La Jolla, LJ-11-02, 40 p.

Teo, S. L. H. 2011. Sensitivity of estimated spawning biomass to natural mortality assumptions 

in Pacific bluefin tuna assessments. ISC/11-1/PBFWG/10. Working document 

submitted to the ISC Pacific Bluefin Tuna Working Group Meeting, 6-13 January 2011. 

Shimizu, Japan. 

Teo, S. L. H. 2011. Updated time series associated with albacore fisheries based in the northeast 

Pacific Ocean. ISC/11/ALBWG/05. Working document submitted to the ISC Albacore 

Working Group Meeting, 30 May–11 June 2011. Shimizu, Japan.

Teo, S. L. H., C. Y. Chen, and T. Matsumoto. 2011. Comparison of length compositions from 

Taiwan longline, Japan pole-and-line, and US longline fisheries. ISC/11/ALBWG/04. 

Working document submitted to the ISC Albacore Working Group Meeting, 30 May–11 

June 2011. Shimizu, Japan.

Teo, S. L. H., V. Tsontos, and S. Kohin. 2011. Preliminary estimated catches of blue and mako 

sharks from US West Coast fisheries. Working document ISC/11/SHARKWG-2/07 

submitted for the ISC Shark Working Group Meeting, 28 November–3 December 2011. 

La Jolla, Calif., USA.

Wells, R. J. D. and S. Kohin. 2011. Length frequencies of the blue shark (Prionace glauca) in 

the eastern Pacific Ocean. Working paper ISC/11/SHARKWG-2/08 submitted for the 

ISC Shark Working Group Meeting, 28 November–3 December 2011. La Jolla Calif., 

USA.

Wells, R. J. D., S. Kohin, S. L. H. Teo, O. E. Snodgrass, and K. Uosaki. 2011. Age and growth 

of North Pacific albacore (Thunnus alalunga). Working paper ISC/11/ALBWG/02 

submitted for the ISC Albacore Working Group Meeting, June 2011. Shimizu, Japan.

Wells, R. J. D., S. E. Smith, S. Kohin, E. Freund, N. Spear, and D. A. Ramon. 2011. Age 

validation of juvenile shortfin mako shark (Isurus oxyrinchus) tagged off southern 

California, USA. Working document ISC/11/SHARKWG-2/06 submitted for the ISC 

Shark Working Group Meeting, 28 November–3 December 2011. La Jolla, Calif., USA.

Approved by the Science Director

Finkbeiner, E. M., B. P. Wallace, J. E. Moore, R. L. Lewison, L. B. Crowder, and A. J. Read. 

Cumulative estimates of sea turtle bycatch and mortality in U.S.A. fisheries between 1990–2007. 

For consideration for publication in Biological Conservation.
37

Griffiths, S. P., R. J. Olson, and G. M. Watters. Complex wasp-waist regulation of pelagic 

ecosystems in the Pacific. For consideration for publication in Reviews in Fish Biology and 

Fisheries.

Kellar, N. M., M. L. Tego, S. J. Chivers, and F. I. Archer. Pregnancy patterns of pantropical 

spotted dolphins (Stenella attenuata) in the eastern tropical Pacific determined from hormonal 

analysis of blubber biopsies and correlations with the purse-seine tuna fishery. For consideration 

for publication in Marine Ecology Progress Series.

Lennert-Cody, C. E., J. D. Rusin, M. N. Maunder, E. H. Everett, E. D. Largacha Delgado, and P. 

K. Tomlinson. Use of tuna size composition data to study small purse-seine vessel fishing 

behavior and implications for dolphin conservation in the eastern tropical Pacific Ocean. For 

consideration for publication in MEPS Inter-Research Science Center.

Moore, J. E. A cautionary note about assessing human impacts on age-structured populations: 

recent examples from sea turtles and fisheries. For consideration for publication in Biological 

Conservation.

Scott, M. S. Chivers, R. Olson, P. Fiedler, and K. Holland. Pelagic predator associations: Tuna 

and dolphins in the eastern tropical Pacific Ocean. For consideration for publication in Marine 

Ecology Progress Series.