Modeling loggerhead sea turtle (Caretta caretta) interactions with US Mid-Atlantic bottom trawl gear for fish and scallops, 2005–2008

Interactions between sea turtles and northwestern Atlantic trawl fisheries are of global concern, and the National Marine Fisheries Service is considering expanding bycatch reduction regulations, including deployment of turtle excluder devices (TEDs). To inform bycatch mitigation strategies, the number of loggerhead sea turtle (Caretta caretta) interactions was estimated for US Mid-Atlantic bottom trawl fisheries for fish and scallops. A generalized additive model of interactions was developed using 1994–2008 Northeast Fisheries Observer Program data from trawl fisheries that were not required to deploy TEDs. Predicted loggerhead interaction rates were applied to 2005–2008 commercial fishing data to estimate the number of interactions for the trawl fleet. For trawl fisheries in which TEDs were required, an experimentally-determined TED exclusion rate (97%) was applied to estimate the number of loggerheads that were excluded by TEDs. Latitude, depth, and sea surface temperature (SST) were associated with the interaction rate. Average annual interactions for 2005–2008 were estimated at 292 (CV 0.13, 95% CI 221–369) loggerheads, with an additional 61 (CV 0.17, 95% CI 41–83) excluded by TEDs. The interaction rate was highest south of latitude 37°N in waters <50 m deep with SST >15 °C; interaction magnitude in terms of adult equivalents was highest at latitude 37–39°N, depth <50 m, and SST >15 °C. Predicted average annual loggerhead interactions decreased compared to 1996–2004, likely due to decreased commercial fishing effort in high-interaction areas. Additional sea turtle conservation measures can be informed by the high-interaction-rate and -magnitude areas identified through this analysis.     

Potential impacts of emerging mahi-mahi fisheries on sea turtle and elasmobranch bycatch species

Mahi-mahi (Coryphaena hippurus) is a resilient pelagic species that could provide long-term highly productive fisheries. Using FAO data we document enormous increases (746%) in reported global mahi-mahi landings since 1950. Detailed mahi-mahi fisheries records are limited, but an observer program monitoring Costa Rica’s Pacific mahi-mahi pelagic longline fleet between 1999 and 2008 (n = 217 sets) provided a rare opportunity to quantify bycatch in these fisheries. Several sea turtles and sharks of global conservation concern were caught incidentally: olive ridley turtle (Lepidochelys olivacea; n = 1348, mean = 9.05 per 1000 hooks), silky shark (Carcharhinus falciformis; n = 402, mean = 2.96 per 1000 hooks), thresher sharks (Alopias sp.; n = 158, mean = 1.12 per 1000 hooks), green turtle (Chelonia mydas; n = 49, mean = 0.35 per 1000 hooks), and three other threatened sharks in small numbers. Pelagic stingray (Pteroplatytrygon violacea; a ray of low conservation concern) was also a common bycatch (n = 625, mean = 4.77 per 1000 hooks). Generalized linear models (GLMs) of catch rates showed increases in olive ridley turtles and decreases in mahi-mahi and silky sharks over the decade examined. The high hooking survival rates of olive ridley and green turtles in observed sets (95% and 96% respectively) suggest that widespread training of the fleet in careful gear removal and turtle release methods could be one effective bycatch mitigation strategy for these species. GLMs also provide evidence that closing the fishery during peak olive ridley nesting times (at least near nesting beaches), in combination with reduced gear soak times, could help minimize the fishery’s impacts on threatened bycatch species while still maintaining a productive fishery.     

An interview-based approach to assess marine mammal and sea turtle captures in artisanal fisheries

Recent case studies have highlighted high bycatch mortality of sea turtles and marine mammals in artisanal fisheries, but in most countries there are few data on artisanal fishing effort, catch, or bycatch. With artisanal fisheries comprising >95% of the world’s fishermen, this knowledge gap presents a major challenge to threatened species conservation and sustainable fisheries initiatives. We report on results from an intensive pilot study to evaluate whether interview surveys can be effective in assessing fishing effort and threatened species bycatch. Fisheries and bycatch data from interviews with >6100 fishermen in seven developing countries were collected in <1 year for approximately USD $47,000, indicating that this approach may rapidly yield coarse-level information over large areas at low cost. This effort provided the first fisheries characterizations for many areas and revealed the widespread nature of high bycatch in artisanal fisheries. Challenges to study design and implementation prevented quantitative estimation or spatial comparisons of bycatch during this pilot research phase, but results suggested that annual sea turtle bycatch may number at least in the low thousands of individuals per country. Annual odontocete bycatch may number at least in the low hundreds per country. Sirenian bycatch occurred in all study areas but was frequent only in West Africa. We discuss lessons learned from this survey effort and present a revised protocol for future interview-based bycatch assessments.     

Bycatch mitigation in context: Using qualitative interview data to improve assessment and mitigation in a data-rich fishery

Bycatch from pelagic longline fisheries has contributed to widespread population declines of turtles, sharks and other pelagic fishes. While large-scale estimates are needed to understand cumulative impacts on these highly migratory species, detailed information on targeting, setting, and discarding practices is needed to develop bycatch mitigation approaches. Data from qualitative fishers’ knowledge interviews with Canadian Atlantic pelagic longline captains was used to evaluate current bycatch estimation methods and to identify bycatch mitigation opportunities. Interviewed longline captains reported blue sharks (Prionace glauca) were common bycatch during swordfish-targeted sets, but were sometimes absent from tuna-targeted sets. Discrepancies between longline captains’ observations and bycatch assessment methods identified needed improvements to data collection methods. Longline captains reported innovative uses of turtle dehooking gear, which two-thirds of interviewed captains had used to release other bycatch species in addition to turtles. Longline captains reported techniques for discarding pelagic stingray (Pteroplatytrygon violacea), a common bycatch species in Pacific, Atlantic and Mediterranean pelagic longline fisheries. Therefore, such techniques could decrease fisheries impacts globally. While there can be major conservation benefits from fishers’ knowledge research, one-quarter of the active longline captains that we contacted declined interviews because they did not trust the larger research process. We urge conservation biologists to carefully design fishers’ knowledge research taking into account the often politicized context. Failure to do so may jeopardize future research and conservation efforts.     

A global assessment of the impact of fisheries-related mortality on shy and white-capped albatrosses: Conservation implications

Hundreds of thousands of seabirds are killed each year as a result of interacting with longline and trawl fishing operations, and the severity of the impact varies regionally. Shy and white-capped albatrosses, Thalassarche cauta and Thalassarche steadi respectively, are phenotypically similar species known to be incidentally killed by fishing operations. The magnitude of this mortality has not previously been assessed across their range. Here we examine recent effort and bycatch rates in fisheries known to incidentally kill these species and qualitatively evaluate the level of impact of each fishery. Results indicate that over 8500 of these albatrosses may be killed annually, although the reliability of this estimate is low due to the paucity of comprehensive observer data in most fisheries. Of the estimated deaths of all seabird species in the fisheries assessed, trawl and longline fisheries killed birds in approximately equal proportions, but when the mortality levels of shy-type albatrosses were examined, trawl fisheries were responsible for 75% of all deaths. Data suggest most of these birds were killed in South African, Namibian and New Zealand demersal trawl fisheries and the South Africa pelagic longline fishery. Because most adult shy albatrosses are comparatively sedentary and rarely found outside Australian waters, it is primarily juvenile shy albatrosses that regularly encounter fishing fleets known to kill large numbers of albatrosses. In contrast, throughout most of their range juvenile and adult white-capped albatrosses are exposed to fisheries that collectively kill many thousands of these albatrosses each year. These data emphasise the urgent need for robust assessments of the impact of bycatch at a species and population level, and the urgent implementation of effective mitigation measures.     

Sea turtle bycatch in the Chilean pelagic longline fishery in the southeastern Pacific: Opportunities for conservation

Data are presented on sea turtles caught in the Chilean longline fishery targeting swordfish, Xiphias gladius, in international waters off Chile. A total of 10,604,059 hooks from 7976 sets were observed, representing 94% of the total number of hooks fished between 2001 and 2005. Leatherbacks, Dermochelys coriacea, (n = 284) and loggerheads, Caretta caretta, (n = 59) were the most common species captured. Leatherbacks were caught in less than 4% of the sets, with an overall mean of 0.0268 turtles per 1000 hooks. Loggerheads were caught in less than 1% of the sets with a mean catch rate of 0.0056 turtles per 1000 hooks. Most leatherbacks (97.5% of total) were caught between 24°S and 38°S, while loggerheads were caught primarily in the northern portion of the area fished, between 24°19′S and 25°31′S. All loggerheads were dehooked where appropriate and released alive. A total of two leatherbacks were found dead. Despite the low catch rate of leatherbacks, the potential impact of this fishery on the severely depleted nesting populations in the eastern Pacific could be significant when combined with other fisheries and threats in the region. The very low mortality of bycaught sea turtles observed in our study is encouraging and suggests that there are opportunities for further reducing harmful effects of swordfish longline fishing on sea turtles. Results of spatial analysis of loggerhead bycatch relative to fishing effort show that closure of the northernmost fishing area would eliminate the majority of the loggerhead bycatch.     

Do circle hooks reduce the mortality of sea turtles in pelagic longlines? A review of recent experiments

Circle hooks have been proposed as a means of reducing the by-catch mortality of sea turtles in pelagic longline fisheries to sustainable levels. I examine the efficacy of circle hooks as a sea turtle conservation measure by examining the results of field trials conducted in the western North Atlantic, the Azores, the Gulf of Mexico, and Ecuador. These experiments employed more than a million and a half hooks between 2000 and 2004 and, in general, were well designed, conducted and analyzed. Four of five experiments demonstrated a significant reduction in capture rate and/or hooking location, indicating that circle hooks would reduce overall mortality. In one trial, however, circle hooks reduced catches of target species to such a degree that their use was impractical. I conclude, therefore, that circle hooks have the potential to reduce the mortality of sea turtles captured in many (but not all) pelagic longline fisheries, but that they should be field tested in a rigorous experiment before they are required in any fishery. Circle hooks will not reduce mortality rates of sea turtles in every pelagic longline fishery; each case needs to be tested before this measure is adopted. Circle hooks reduce turtle mortality because of their shape and size and the ways that these parameters interact with the size of turtles interacting with the fishery. Circle hooks may cause a reduction in turtle mortality by decreasing the incidence of hook ingestion as well as reducing capture rate, particularly for loggerhead sea turtles.     

Pelagic longlines: A threat to sea turtles in the Equatorial Eastern Atlantic

Pelagic longlines are widely known to interact with several species of sea turtles, and there is an increasing concern about the by-catch of turtles in commercial fisheries and its impact on their populations. However, information on sea turtle by-catch in the South Atlantic Ocean is scarce, and there are no quantitative by-catch data available on olive ridleys for the Equatorial Eastern Atlantic. In this paper we analyze data collected by observers on board an Uruguayan long-liner targeting swordfish in two areas in the Equatorial Eastern Atlantic: off the Gulf of Guinea and north of Saint Helenaa Island. Specimens of Lepidochelys olivacea and Dermochelys coriacea were hooked or entangled in 26 longline sets. All registered interactions with olive ridleys took place off the The Gulf of Guinea, with captures ranging from 1 to 3 specimens in a single set. The captured specimens, though not measured directly, appeared to be juveniles. In addition, the examination of the stomach contents of one female mako shark showed dermal scutes, vertebrae and the complete head of a sea turtle identified as L. olivacea, allowing us to estimate its curved carapace length. In contrast, adult specimens of D. coriacea were caught in the two fishing areas. The capture of 10 individuals in a single set was recorded. Due to the high rate of sea turtle by-catch observed off the The Gulf of Guinea (1.02 ind/1000 hooks) conservation programs in the area should take into consideration the possible existence of a developmental and feeding area in this zone. Accordingly, longline fisheries in this area should be monitored and mitigation measures put in place to avoid or minimize damage to the pelagic phase of African populations of sea turtles.     

From both sides: Dire demographic consequences of carnivorous mice and longlining for the Critically Endangered Tristan albatrosses on Gough Island

The IUCN recently uplisted the Tristan albatross (Diomedea dabbenena) to Critically Endangered. Here we present new data indicating negative population trends on Gough Island arising from low adult survival (∼91%, ascribed to accidental mortality on fishing gear) and low breeding success (averaging 32%, due to mouse predation). Fledgling production from 1979 to 2007 and numbers of incubating adults from 1956 to 2007 have both decreased by ∼1% p.a. Consecutive annual counts of incubating adults and a population model permit the first reliable estimates of the Tristan albatross population, presently 5400 breeding adults and 11,300 birds in all age- and stage-classes. Population models explore scenarios of likely demographic trends using combinations of hypothetical best-case estimates vs. observed estimates for two key parameters: adult survival and breeding success. These scenarios highlight the relative benefits to the species of eradicating mice or mitigating bycatch. The model scenario using observed estimates predicts annual growth rate at −2.85%. Adult survival rates have probably decreased in recent years, concomitant with increased longline fishing effort, which might explain the discrepancy between counts and modelled trends. Negative trends cannot be reversed by improving breeding success alone, and adult survival must exceed an improbable 97% to balance the current chick production. A worst-case scenario including a fixed number of adult deaths annually predicted a catastrophic 4.2% p.a. decrease and extinction in ∼30 years. Population growth was most sensitive to adult survival, but even using an adult survival estimate without fishery mortality, current breeding success is insufficient to maintain the population. These findings do not support the ‘compensatory mitigation of bycatch’ model (offsetting bycatch impacts by eradicating invasive species), and the impacts of both fishery mortality and mouse predation must be addressed to improve the conservation status of the Critically Endangered Tristan albatross.     

At-sea distribution of breeding Tristan albatrosses Diomedea dabbenena and potential interactions with pelagic longline fishing in the South Atlantic Ocean

The endangered Tristan albatross Diomedea dabbenena is restricted to Gough and Inaccessible Islands. The species is killed as bycatch by longline fisheries in the South Atlantic, but the impact of this mortality is unknown. We satellite tracked 38 breeding Tristan albatrosses and assessed the seasonal and annual at-sea distribution of these birds in relation to reported pelagic longline fishing effort. These birds ranged across the South Atlantic from 50°W to 15°E with most (97%) daytime satellite fixes between latitudes 30°S and 45°S. Considerable fishing effort occurred within the same latitudes. Although there was no correlation between their at-sea distributions, there was a broad overlap between birds and fishing effort. Estimated bycatch rates for Tristan albatross and other Diomedea species in the South Atlantic, and the spatio-temporal overlap between birds and hooks, yield a predicted annual mortality of 471-554 birds, sufficient to cause population decreases of 3.6-4.3% per year. An index of bird × hook interactions (proportional density of birds multiplied by number of hooks by decadal period for each 5° square of longitude and latitude) indicated that 47% of annual interactions occurred in areas around Gough Island, and 11% and 15% of interactions in areas of the west and east Atlantic, respectively. There were also within seasonal differences in the key areas of overlap. The fishing fleets of Taiwan and Japan are likely to be responsible for most interactions based upon the reported magnitude of effort expended in the South Atlantic by these fleets. Ensuring that licensed fishing vessels within the Tristan da Cunha Exclusive Economic Zone (EEZ) operate using best-practise mitigation measures and with fisheries observer programs, could reduce the potential bycatch mortality of breeding Tristan albatrosses in this region by nearly one third. Thorough implementation of international agreements is required in areas of the high seas where most remaining interactions are predicted to occur.     

Estimating incidental takes of shearwaters in driftnet fisheries: lessons for the conservation of seabirds

We consider estimation of the magnitude of incidental fisheries ‘bycatch’ for two petrel species, sooty shearwaters (Puffinus griseus) and short-tailed shearwaters (Puffinus tenuirostris). There are clear statistical advantages in estimating bycatch for abundant species such as these, and our results may also guide the conservation and management of rarer species. We used fisheries statistics and observer data to estimate retrospectively the total numbers of sooty and short-tailed shearwaters bycatch in seven large-scale pelagic North Pacific driftnet fisheries between 1952 and 2001. Sensitivity analysis greatly simplified estimation of uncertainty by identifying four driftnet fisheries to be of particular importance in determining the magnitude and precision of the estimated bycatch totals. We estimated that between 1.0 and 12.8 million (95% CI) sooty shearwaters were killed by driftnets between 1952 and 2001. For short-tailed shearwaters we estimated between 4.6 and 21.2 million (95% CI) over the same period. More precise estimation was hampered by the paucity of available observer data, lack of reported detail and inconsistencies among data sources. Estimates may be strongly biased because some dead birds are misidentified or drop out of nets before hauling, or because some records were of live captures that were subsequently released. Improved estimation of overall take and its impact on populations of seabirds requires standardisation of reporting, allowance for potential sampling bias, as well as a clearer definition of the sampling unit and underlying bycatch probability distribution model, and knowledge of potential compensatory changes in population parameters.     

Understanding and addressing seabird bycatch in Alaska demersal longline fisheries

The incidental catch of seabirds in longline fisheries is a global conservation concern. In Alaska, annual seabird bycatch in demersal longline fisheries ranged between 10,300 and 26,300 birds (1995–2001). We explore the relationship between four categories of potential forcing factors (temporal, spatial, environmental, and fisheries-related) and seabird bycatch rates in Alaska demersal longline fisheries to provide practical management alternatives that could significantly reduce seabird bycatch.Separate generalized linear or additive models (GLM or GAM, respectively) were created for several combinations of seabird group, fishery and large geographic region. Across nearly all models, “vessel” was the most influential factor explaining seabird bycatch rate variation. Rather than a single variable, vessel is an amalgam of unmeasured forcing factors many of which could not be separated out in this data set (e.g., longline sink rate, vessel setting speed, line deployment location relative to propeller direction). A separate vessel-specific analysis also supported the multivariate results that performance of an individual vessel is overwhelmingly important (i.e., some vessels have consistently high or low bycatch rates from year to year). Therefore, vessel-specific performance is a critical management option.The effects of temporal (annual, month, and breeding phenology) and spatial variables were also moderately influential on seabird bycatch rates. Our results suggest that seasonal adjustments in the Alaska longline fishery have potential for overall bycatch reductions, but vague seabird management objectives could have huge unintended and undesirable consequences when implementing temporal adjustments. Other variables (environmental and other fishing-related factors) were frequently significant but contributed a small amount to overall explained deviance.Based on this study, we conclude that a vessel-specific management approach would be the most effective and efficient means to reduce seabird bycatch in Alaska.     

Incidental and intentional catch threatens Galápagos waved albatross

As large, long-lived seabirds with delayed and slow reproduction, albatrosses have low intrinsic mortality rates and are especially vulnerable to extinction from extrinsic sources of mortality such as fishery bycatch. Leg-band recovery information for waved albatrosses revealed mortality from both incidental catch and intentional catch for human consumption. Annual adult survival in 1999-2005, estimated from capture-mark-recapture data, was lower than historical estimates. This recent increase in adult mortality probably contributed to recent and dramatic shrinkage of the breeding population; periodic matrix models confirm that population growth rate is most sensitive to changes in adult survival. Banding data and recovery information also suggest that capture by fisheries is male-biased, which should reduce fecundity in this species with obligate bi-parental care. This new documentation of bycatch, harvesting, and associated demographic consequences provides reason for serious concern about the persistence of the single breeding population of the waved albatross.     

Sea turtle by-catch in pelagic longline sets off southern Brazil

Results are presented on sea turtle by-catch observed in pelagic longline sets during research cruises in the south Atlantic in the vicinity of the shelf edge break in southern Brazil. The longline gear was set in a similar manner to that employed by the commercial longline fleet operating out of Santos, Brazil that targets swordfish, Xiphias gladius. Nineteen sea turtles were caught on 14 of 41 sets, which constituted a catch rate of 1.5 turtles per 1000 hooks. Thirty four percentage of all sets captured at least one turtle. The catch included loggerhead, Caretta caretta, leatherback, Dermochelys coriacea, and most likely olive ridley, Lepidochelys olivacea. All turtles, except one loggerhead, were captured live and released. Captures occurred during spring, summer and winter suggesting a year around presence and vulnerability. Given increased levels of longline effort directed at swordfish in the southeast Atlantic, substantial turtle by-catch can be expected. There is a critical need for additional information to be able to assess the potential impact on swordfish longline fisheries on sea turtle populations.     

Estimates of sea turtle mortality from poaching and bycatch in Bahía Magdalena, Baja California Sur, Mexico

Bahia Magdalena on the Pacific coast of Baja California Sur, Mexico, is an important feeding and nursery ground for black turtles Chelonia mydas, loggerhead turtles Caretta caretta, olive ridley turtles Lepidochelys olivacea, and hawksbill turtles Eretmochelys imbricata. Despite international and national protection, sea turtles continue to be caught incidentally and hunted for consumption in large numbers. This study examines the mortality of sea turtles in Bahia Magdalena, focusing on (1) species distribution and number of carcasses found, (2) causes of death, (3) size frequency distribution and % juveniles in the catch, and (4) changes in average size over the past years. A total of 1945 turtle carcasses were found from April 2000 to July 2003 along beaches and in towns of the region with loggerhead (44.1%) and black turtles (36.9%) being the dominant species. Slaughter for human consumption was the primary cause of death of carcasses found in towns (95-100%), while carcasses on beaches mostly died of unknown causes (76-100%). Circumstantial evidence suggests however, that incidental bycatch was the main mortality cause on beaches. Black turtles suffered the highest consumption mortality overall (91%), followed by olive ridley (84%), hawksbill (83%) and loggerhead turtles (63%). Over 90% of all turtles found were juveniles or subadults. Carapace length of black turtles declined consistently over the sampling period, while that of loggerhead turtles increased. Our results strongly suggest that turtles are being taken at high and unsustainable rates; this may partially explain why the populations have not recovered despite widespread protection on nesting beaches.     

The impact of pelagic longline fishing on the flesh-footed shearwater Puffinus carneipes in Eastern Australia

The flesh-footed shearwater (Puffinus carneipes) is a medium-sized seabird (ca. 700 g) that is incidentally killed during longline fishing operations. We examined the levels of bycatch in Australia’s Eastern Tuna and Billfish Fishery and developed a model to examine the impact of this fishery on the eastern Australian population of flesh-footed shearwaters, which breeds at only one site, Lord Howe Island. Observed bycatch rates for flesh-footed shearwaters were 0.378 birds/1000 hooks for night sets, and 0.945 birds/1000 hooks for day sets. The mean number of birds killed from 1998 to 2002 was estimated to be 1794-4486 birds per year, with the estimated total killed over this period ranging from 8972 to 18,490 birds. Models incorporating both density-independent and density-dependent scenarios were applied to levels of bycatch representative of that observed in the fishery. Density-independent scenarios showed that fishing mortality levels caused declines in the majority of simulated populations. In contrast, density-dependent scenarios produced populations that were more resilient to fishing mortalities. Although some modelling scenarios led to population growth, under most stochastic simulations median population halving and quasi-extinction times were less than 55 and 120 years, respectively. We conclude that the level of bycatch observed in the fishery is most likely unsustainable and threatens the survival of the Lord Howe Island population. This situation can be improved only with the development and implementation of mitigation measures that will halt or greatly reduce the level of bycatch currently observed. Improved knowledge on a range of demographic parameters for the species, combined with a clearer idea of the at-sea distribution of breeding and non-breeding shearwaters, will greatly assist in improving understanding and the management of this population.     

Assessing the susceptibility of female black-footed albatross (Phoebastria nigripes) to longline fisheries during their post-breeding dispersal: an integrated approach

Albatross movements and foraging grounds during the post-breeding dispersal are poorly understood, despite their important conservation implications. We tracked four female black-footed albatrosses (Phoebastria nigripes) for 100 days during their summer (July-September, 1997-1999) post-breeding dispersal off California, and compared their movements to the distribution of fishing effort from the Japanese Eastern Pacific Ocean (EPO) longline fishery. The tracked birds foraged largely along the transition zone between the California Current and the Central Pacific Gyre, and spent 25, 24, and 51% of their time at sea within the 200-mile exclusive economic zones (EEZs) of the USA and Mexico, and the high seas (international waters) respectively. The satellite-tracked birds occupied subtropical waters (18-20 °C) targeted by longline fisheries for tuna (Thunnus spp.) and broad-bill swordfish (Xiphias gladius), and ranged disproportionately farther during daylight hours, when tuna fisheries operate. The available data suggest that albatrosses overlap temporally and spatially with longline fisheries in the northeast Pacific Ocean. However, this research cannot directly evaluate whether black-footed albatross bycatch occurs in these fisheries. The coarse temporal (monthly) and spatial (1°×1°) resolution of the fisheries data, and the dynamic nature of the fishing effort inhibited a fine-scale analysis of albatross overlap with longline fisheries. While we documented substantial spatial overlap between albatross distributions and the Japanese EPO longline fishing effort during the 1980s, we found no co-occurrence during the 1990s. This study illustrates the value of satellite telemetry to assess national conservation responsibilities, and to identify potential interactions of protected species with fisheries not currently monitored by observer programs. Furthermore, our results underscore the need to exercise caution when interpreting satellite telemetry data for conservation purposes, because of the highly dynamic nature of pelagic fisheries.     

Interpreting the spatio-temporal patterns of sea turtle strandings: Going with the flow

Knowledge of the spatial and temporal distribution of specific mortality sources is crucial for management of species that are vulnerable to human interactions. Beachcast carcasses represent an unknown fraction of at-sea mortalities. While a variety of physical (e.g., water temperature) and biological (e.g., decomposition) factors as well as the distribution of animals and their mortality sources likely affect the probability of carcass stranding, physical oceanography plays a major role in where and when carcasses strand. Here, we evaluate the influence of nearshore physical oceanographic and wind regimes on sea turtle strandings to decipher seasonal trends and make qualitative predictions about stranding patterns along oceanfront beaches. We use results from oceanic drift-bottle experiments to check our predictions and provide an upper limit on stranding proportions. We compare predicted current regimes from a 3D physical oceanographic model to spatial and temporal locations of both sea turtle carcass strandings and drift bottle landfalls. Drift bottle return rates suggest an upper limit for the proportion of sea turtle carcasses that strand (about 20%). In the South Atlantic Bight, seasonal development of along-shelf flow coincides with increased numbers of strandings of both turtles and drift bottles in late spring and early summer. The model also predicts net offshore flow of surface waters during winter - the season with the fewest relative strandings. The drift bottle data provide a reasonable upper bound on how likely carcasses are to reach land from points offshore and bound the general timeframe for stranding post-mortem (< two weeks). Our findings suggest that marine turtle strandings follow a seasonal regime predictable from physical oceanography and mimicked by drift bottle experiments. Managers can use these findings to reevaluate incidental strandings limits and fishery takes for both nearshore and offshore mortality sources.     

Post-breeding season distribution of black-footed and Laysan albatrosses satellite-tagged in Alaska: Inter-specific differences in spatial overlap with North Pacific fisheries

We integrated satellite-tracking data from black-footed albatrosses (Phoebastria nigripes; n = 7) and Laysan albatrosses captured in Alaska (Phoebastria immutabilis; n = 18) with data on fishing effort and distribution from commercial fisheries in the North Pacific in order to assess potential risk from bycatch. Albatrosses were satellite-tagged at-sea in the Central Aleutian Islands, Alaska, and tracked during the post-breeding season, July-October 2005 and 2006. In Alaskan waters, fishing effort occurred almost exclusively within continental shelf and slope waters. Potential fishery interaction for black-footed albatrosses, which most often frequented shelf-slope waters, was greatest with sablefish (Anoplopoma fimbria) longline and pot fisheries and with the Pacific halibut (Hippoglossus stenolepsis) longline fishery. In contrast, Laysan albatrosses spent as much time over oceanic waters beyond the continental shelf and slope, thereby overlapping less with fisheries in Alaska than black-footed albatrosses. Regionally, Laysan albatrosses had the greatest potential fishery interaction with the Atka mackerel (Pleurogrammus monopterygius) trawl fishery in the Western Aleutian Islands and the sablefish pot fishery in the Central Aleutian Islands. Black-footed albatrosses ranged further beyond Alaskan waters than Laysan albatrosses, overlapping west coast Canada fisheries and pelagic longline fisheries in the subarctic transition domain; Laysan albatrosses remained north of these pelagic fisheries. Due to inter-specific differences in oceanic distribution and habitat use, the overlap of fisheries with the post-breeding distribution of black-footed albatrosses is greater than that for Laysan albatrosses, highlighting inter-specific differences in potential vulnerability to bycatch and risk of population-level impacts from fisheries.     

Reducing incidental mortality of seabirds with an underwater longline setting funnel

A demersal longline fishery for Patagonian toothfish (Dissostichus eleginoides) that commenced off the Prince Edward Islands during 1996 has killed significant proportions of locally breeding albatrosses and petrels. As one of a suite of mitigation measures, we tested the efficacy of a Mustad underwater setting funnel to reduce incidental mortality of seabirds. The funnel, which deploys the longline 1-2 m beneath the sea surface, was used on 52% of 1714 sets (total effort 5.12 million hooks) over a 2-year period. Used in conjunction with a bird-scaring line, overall seabird bycatch rate was low (0.022 birds per 1000 hooks), and was dominated by white-chinned petrels (Procellaria aequinoctialis) (88% of the 114 birds killed). Bycatch rate was three times lower when the funnel was used both by day and at night. Daytime catch rates with the funnel were less than those attained during night sets without the funnel. In conjunction with other mitigation measures, underwater setting offers a significant reduction in seabird mortality in this fishery and could increase fishing efficiency by allowing daytime setting. However, small numbers of albatrosses were caught during daytime sets with the funnel, and its use for daytime sets should be closely monitored.