Adaptive spatiotemporal management to reduce shark bycatch in tuna fisheries.

Accurate assessment of shark population status is essential for conservation but is often constrained by limited and unreliable data. To provide a basis for improved management of shark resources, we analyzed a long-term record of species-specific catches, sizes, and sexes of sharks collected by onboard observers in the western and central Pacific Ocean from 1995 to 2010. Using generalized linear models, we estimated population-status indicators on the basis of catch rate and biological indicators of fishing pressure on the basis of median size to identify trends for blue (Prionace glauca), mako (Isurus spp.), oceanic whitetip (Carcharhinus longimanus), and silky (Carcharhinus falciformis) sharks. Standardized catch rates of longline fleets declined significantly for blue sharks in the North Pacific (by 5% per year [CI 2% to 8%]), for mako sharks in the North Pacific (by 7% per year [CI 3% to 11%]), and for oceanic whitetip sharks in tropical waters (by 17% per year [CI 14% to 20%]). Median lengths of silky and oceanic whitetip sharks decreased significantly in their core habitat, and almost all sampled silky sharks were immature. Our results are consistent with results of analyses of similar data sets. Combined, these results and evidence of targeted fishing for sharks in some regional fisheries heighten concerns for sustainable utilization, particularly for oceanic whitetip and North Pacific blue sharks. Regional regulations that prohibit shark finning (removal of fins and discarding of the carcass) were enacted in 2007 and are in many cases the only form of control on shark catches. However, there is little evidence of a reduction of finning in longline fisheries. In addition, silky and oceanic whitetip sharks are more frequently retained than finned, which suggests that even full implementation of and adherence to a finning prohibition may not substantially reduce mortality rates for these species. We argue that finning prohibitions divert attention from assessing whether catch levels are sustainable and that the need for management of sharks should not be addressed by measures that are simple to implement but complex to enforce and evaluate.

Shark bycatch represents a substantial issue in the management of oceanic fisheries. Utilizing data on shark bycatch from the longline fishery, as released by the Western and Central Pacific Fisheries Commission, this study applied the boosted regression tree model to examine the impact of environmental factors on the bycatch per unit effort (BPUE) of key bycatch species, as well as to predict the spatial distribution dynamics of both BPUE and bycatch risk (BR). The findings emphasize that the oxygen concentration, sea surface temperature, and chlorophyll-a concentration are paramount to sharks’ BPUE. Furthermore, the study compared the variations in environmental preferences across diverse shark species, pinpointing key environmental attributes defining the ecological niches of distinct shark populations. The spatial predictions identified the hotspots of BPUE and BR for the bigeye thresher shark (Alopias superciliosus), longfin mako (Isurus paucus), silky shark (Carcharhinus falciformis), and oceanic whitetip shark (Carcharhinus longimanus) in tropical latitudes (10° S to 15° N), and for the blue shark (Prionace glauca) and shortfin mako (Isurus oxyrinchus) in temperate zones (south of 30° S or north of 30° N). The geometric center analysis indicated that all shark species exhibited large annual fluctuations in BPUE and BR, and most populations displayed significant shifting trends. Several grids (5° × 5°) were identified as high-risk areas due to their considerable contribution to bycatch. Furthermore, the geometric centers of BR were observed to shift eastward towards equatorial waters, compared to the geometric centers of BPUE. This underscores the necessity of considering factors beyond BPUE when identifying critical areas for the implementation of area-specific bycatch mitigation measures. The insights derived from this study can enhance and support the development and enforcement of targeted area-based fishery management initiatives.

Populations of northeastern offshore spotted dolphins Stenella attenuata attenuata and eastern spinner dolphins S. longirostris orientalis have been reduced because the dolphins are bycatch in the purse-seine fishery for yellowfin tuna in the eastern tropical Pacific Ocean (the 'tuna-dolphin issue'). Abundance and trends of these dolphin stocks were assessed from 12 large-scale pelagic surveys carried out between 1979 and 2000. Estimates of abundance were based on a multivariate line-transect analysis, using covariates to model the detection process and group size. Current estimates of abundance are about 640 000 northeastern offshore spotted dolphins (CV = 0.17) and 450 000 eastern spinner dolphins (CV = 0.23). For the whole period from 1979 to 2000, annual estimates of abundance ranged from 494 000 to 954 000 for northeastern offshore spotted dolphins and from 271000 to 734 000 for eastern spinner dolphins. Management actions by USA and international fishing agencies over 3 decades have successfully reduced dolphin bycatch by 2 orders of magnitude, yet neither stock is showing clear signs of recovery. Possible reasons include underreporting of dolphin bycatch, effects of chase and encirclement on dolphin survival and reproduction, long-term changes in the ecosystem, and effects of other species on spotted and spinner dolphin population dynamics.

The silky shark is important in commercial fisheries, but their population has declined in recent years. One of the major challenges for species under this scenario is to understand their trophic interactions as they grow and to apply this knowledge for their management and protection. Based on the analysis of δ15N and δ13C in muscle and vertebral tissue, the aim of this study is to assess the feeding habits (possible changes in resource and habitat use) of C. falciformis related to ontogeny (neonatal, juvenile, and adult stages), which may lead to the reassessment of the species’ trophic role in the Eastern Tropical Pacific Ocean (ETPO). The isotopic composition of muscle (n = 60) and vertebrae (n = 44) was analyzed over 3 years (2003–2005). Significant differences were detected in δ15Nmuscle between neonates and juveniles (H = 6.26, p < 0.05) and in δ13Cmuscle between juveniles and adults (H = 6.78, p < 0.05). Significant differences were detected also in δ15Nvertebrae (F = 4.19, p < 0.05) and δ13Cvertebrae (F = 6.59, p < 0.05) among ontogenetic stages, particularly regarding females (H = 34.77, p < 0.05), which may indicate: 1) that they consume different prey types as a result of changing energy requirements linked to their ontogeny (e.g., reproduction), and 2) different movement patterns. If the estimated trophic position of C. falciformis was 3.7, then the species could be classified as a tertiary predator. The data generated in this study indicate ontogenetic changes in the feeding behavior of C. falciformis, which is critical to understanding the role of this predator in the community structure of the ETPO.

Large pelagic sharks are distributed throughout all of the oceans and are caught as bycatch in pelagic longline fisheries worldwide. In the southern Atlantic Ocean, more than a dozen shark species are caught by the Brazilian tuna longline fleet. This study compiles information of the main shark species caught by the Brazilian tuna longline fishery in the southwestern and equatorial Atlantic Ocean. Catch and effort data of 14,860 longline sets from the Brazilian chartered tuna longline fleet, between 2004 and 2010, were analyzed. The blue shark Prionace glauca was the main shark species captured by this fishery. Shark catches showed contrasting trends during the study period: the silky (Carcharhinus falciformis) and the oceanic whitetip (C. longimanus) sharks catch increased up to 2008 and then declined, while mako sharks (Isurus spp.) showed an opposite trend. Effort for the Brazilian longline fishery had a higher concentration from 10°N to 30°S and from 20°W to 40°W. High values of catch per unit effort of southwestern and equatorial Atlantic Ocean sharks were heterogeneously distributed and, although elasmobranchs were caught over most of the longline fishing range, only blue sharks were caught in all areas. In the southern Atlantic Ocean, high fishing effort zones overlap significantly with some nursery areas, especially for the oceanic whitetip shark, indicating that these areas are at a direct risk from the industrial longline fishery.

Shark fishery is one of the most important activities in the Mexican Pacific coast, nevertheless, there is few data available about the specific captures done by the fleet along the coast. This study describes fishery biology aspects of the shark species catched by the semi-industrial long-line fleet of Manzanillo. Monthly samplings were made on board of these vessels during an annual period from April 2006 to April 2007. Captured species composition (n = 1 962 organisms) was represented by nine species. The one that sustains this fishery was Carcharhinus falciformis (88.12%), followed by Prionace glauca (8.21%). Low frequency species were represented by Sphyrna zygaena (1.78%), Alopias pelagicus (0.82%), Carcharhinus longimanus (0.45%). Furthermore, rare species were Alopias superciliosus (0.35%), Carcharhinus leucas (0.1%), Carcharhinus limbatus (0.1%) and Isurus oxyrinchus (0.05%). Fishery activity affected principally (60-92.70%) young males of C. falciformis, S. zygaena, C. longimanus and I. oxyrinchus; adult males (56-75%) of A. pelagicus, A. superciliosus, and C. limbatus; for P. glauca there were primarily female adults. For all the species found, females showed the bigger sizes when compared to males (with the exception of S. zygaena, that showed sexual dimorphism). Considering the lineal regressions made between precaudal length and total length, and, fork length and total length for C. falciformis, P. glauca, S. zygaena and A. pelagicus, the determination coefficients (r2) showed that both lengths can be useful to obtain the total length of fish with some damage or absence of its caudal fin. The estimated fecundity for C. falciformis was of 3-7 offspring/female of 30-45 cm LT (average of 40.57 +/- 2.03 cm LT); and for P. glauca 5-52 offspring/female of 5-18.6 cm LT (average of 11.61 +/- 0.21 cm LT). In the case of C. longimanus only one female was captured with a total of eight embryos, with an average of 45 cm LT each; for this reason we assumed that the fishery areas do not coincide with the nursery oness for this species. According to the information obtained, we concluded that C. falciformis has a concurrent cycle and P. glauca a consecutive biannual one.

172. This dispute arises out of a challenge brought by Mexico against certain legal instruments of the United States establishing the conditions for the use of a “dolphin-safe” label on tuna products. In particular, Mexico identified the following legal instruments as the object of its challenge: the United States Code, Title 16, Section 1385 (the “Dolphin Protection Consumer Information Act” or “DPCIA”); the United States Code of Federal Regulations, Title 50, Section 216.91 and Section 216.92 (the “implementing regulations”); and a ruling by a US federal appeals court in Earth Island Institute v. Hogarth (the “Hogarth ruling”). Taken together, the DPCIA, the implementing regulations, and the Hogarth ruling set out the requirements for when tuna products sold in the United States may be labelled as “dolphin-safe”. More specifically, they condition eligibility for a “dolphin-safe” label upon certain documentary evidence that varies depending on the area where the tuna contained in the tuna product is harvested and the type of vessel and fishing method by which it is harvested. In particular, tuna caught by “setting on” dolphins is currently not eligible for a “dolphin-safe” label in the United States, regardless of whether this fishing method is used inside or outside the Eastern Tropical Pacific Ocean (the “ETP”). The DPCIA and the implementing regulations also prohibit any reference to dolphins, porpoises, or marine mammals on the label of a tuna product if the tuna contained in the product does not comply with the labelling conditions spelled out in the DPCIA.

Investigating the relationship between species and environmental conditions is key for the correct management of highly migratory large pelagic species like silky shark (Carcharhinus falciformis). This species is currently ranked as vulnerable by the International Union for Conservation of Nature and the population trend may be decreasing globally. Tuna fisheries annually catch around 5 million tons worldwide but may have effects on the ecosystem, including impacts on certain sensitive non-target species. We provide the first insights into the environmental preferences of silky shark in the Atlantic Ocean by modelling their presence from tropical tuna purse seine observer data (~ 7500 fishing sets between 2003 and 2015) with a set of biotic and abiotic oceanographic factors, spatial–temporal terms and fishing operation variables. Oceanographic data (sea surface temperature, sea surface temperature change, salinity, sea surface height, chlorophyll-a, chlorophyll-a change, oxygen, and current information such as speed, direction and eddy kinetic energy) were downloaded and processed from the EU Copernicus Marine Environment Monitoring Service. Results provide information on the hotspots dynamics of silky shark as well as its habitat preferences. Models detected a significant relationship between seasonal upwelling events, mesoscale features and silky shark presence and suggested strong interaction between productive systems and the spatial–temporal distribution of the species. The model also highlighted both persistent (i.e. Gabon) and temporary areas (i.e. Guinea and southern-central tropical Atlantic Ocean) for silky shark in the region. This information could be used to assist tuna regional fisheries management organizations in the conservation and management of this vulnerable non-target species.

ABSTRACTThe silky shark (Carcharhinus falciformis) has the highest bycatch in gillnets, longlines, and purse seine globally. Its thermal and depth preferences coincide with the tropical tuna habitat, indicating a high capture vulnerability by these fisheries. The present research seeks to determine the environmental conditions that favor silky shark distribution and identify the areas with the highest probability of occurrence. The data analyzed correspond to silky shark bycatch records in the Eastern Pacific Ocean (EPO) published by the Inter‐American Tropical Tuna Commission from 2009 to 2019. The dataset contains information about bycatch (number of organisms), the number of sets made, as well as the fishing indicator (schools not associated [NOA], associated with dolphins [DEL], and with floating objects [OBJ]). The environmental variables sea surface temperature (SST), sea surface height (SSH), mixed layer depth (MLD), chlorophyll‐a (Chl‐a), and dissolved oxygen (DO) concentrations were considered to perform a Bayesian Additive Regression Trees (BART) to model the entire species range distribution. The best‐fitted model included MLD as the most informative variable, followed by Chl‐a concentration and SSH. BART model identified the highest presence probabilities in the oceanic area between 15°S and 10°N and −110°W to −150°W, along the North Equatorial Current and around French Polynesia. The BART model results offer significant insights into silky sharks in the EPO, showing that the equatorial and oceanic areas are the most important for its distribution, supporting the findings from previous studies. This information is crucial for developing effective management strategies to reduce silky shark bycatch.

Projected impacts of ocean warming on pelagic ecosystems in the Western and Central Pacific Ocean using a multi-species size-spectrum model.

Whale sharks (Rhincodon typus) are found circumglobally in tropical, subtropical, and warm temperate waters, and their known seasonal aggregations and migratory movements are influenced by factors such as ocean currents, thermobiological systems, and patterns of productivity. Several locations in the eastern tropical Pacific Ocean are known habitats for R. typus; Although it has long been known that whale sharks aggregate along the Panama coast, little is known in relation to their movement patterns, behavior, and habitat use. In this study, we investigated the movements and behaviors of R. typus tagged in Panama in relation to oceanographic variables and examined the overlap of foraging habitat and migratory routes with marine protected areas (MPAs), industrial fishing areas, and marine traffic. Satellite tracks from 30 R. typus tagged in the coastal waters of Panama were examined, including nine tags suspicious of earlier detachment. A hidden Markov model was then used to identify different behavioral states (foraging and migrating) and their relationships with environmental variables (sea surface temperature, primary productivity, chlorophyll-a concentrations, and eddy location/speed) Tracks were also superimposed on maps of MPAs, industrial fishing areas, and regional marine vessel traffic to identify the degree of overlap. Rhincodon typus foraged mainly within the Panamanian exclusive economic zone but also moved north and south along the coast and out to the open ocean. Significant differences in environmental conditions were found between sites in which foraging and migrating behaviors were recorded. Higher productivity and chlorophyl concentration were associated with foraging behavior, while higher eddy speeds were observed when sharks migrated. Rhincodon typus used MPAs; however, there was a high degree of overlap between their habitat and areas of industrial fishing and marine vessel traffic. Our results highlight the use of the coastal waters of Panama, oceanic seamounts, and ridges, MPAs and industrial fishing areas by R. typus for foraging and migration. Additionally, our findings highlight the importance of satellite tracking studies for understanding the behavior and habitat use of highly mobile migratory species, such as R. typus.

Association dynamics of tuna and purse seine bycatch species with drifting fish aggregating devices (FADs) in the tropical eastern Atlantic Ocean

Measuring abundance of invertebrate forage for piping plovers (Charadrius melodus; hereafter plovers), a federally listed species in the USA, is an important component of research and monitoring targeted toward species recovery. Sticky traps are commonly used to passively sample invertebrates, but catch rates may vary diurnally or in response to weather. We examined diurnal variation in catch rates of invertebrates using an experiment on reservoir shoreline and riverine sandbar habitats of the Upper Missouri River in 2006 and 2008. Highest catch rates of large invertebrates (>3 mm) on dry sand habitats occurred during 08:00–11:00 Central Daylight Time (CDT) on the reservoir and 08:00–14:00 CDT on the river. On wet sand habitats, catch rates were lowest during 17:00–20:00 on both the reservoir and the river. Catch rates decreased 24% for every 10 kph increase in wind. Sticky traps deployed continuously for 12 h or more had lower catch rates than four consecutive-composited 3-hour deployments, suggesting that trap effectiveness declined for >3-hour deployments. Thus, if sticky traps are used to index plover forage abundance without controlling for time of day and wind speed, data may be highly variable or estimates could be biased.

Movements and habitat use of juvenile silky sharks in the Pacific Ocean inform conservation strategies

Tuna is one of the important export commodities to increase government income. One of economically important tuna species is bigeye tuna (Thunnus obesus) which has a proportion of 21% of the total production of large tuna group. The objective of this study was to investigate the effects of different moon phase on the catch of bigeye tuna (T. obesus) in Eastern Indian Ocean. Data collection was conducted by the scientific observers from August 2005 to June 2014 in the tuna longline vessels were based in the port of Benoa, Bali. Moon phase data were collected from August 2005 to June 2014 from National Aeronautics and Space Administration (NASA). Catch data were calculated using the catch rate formula which defined as the number of catches per 100 hooks. The number of catch rate then was sorted into each moon phases and were analyzed using one-way Anova. This study covered 62 trips and 1,480 numbers of operations or sets was conducted from sampled vessels. The result showed that the average catch rate of bigeye tuna differed significantly among the moon phases. Tukey post-hoc tests showed that the average catch rate at full moon was the highest among the groups with around 0.3/100 hooks. This study showed that moon phase had significant effect on the catch of bigeye tuna (T. obesus) that increased the catch during full moon. Keywords: moon phase, catch rate, Eastern Indian Ocea, tuna, Thunnus obesus