Subsurface behavior of bottlenose dolphins (Tursiops truncatus) interacting with fish trawl nets in northwestern Australia: Implications for bycatch mitigation

Most studies of delphinid‐trawler interactions have documented the surface behavior of dolphins feeding on discarded bycatch, but not their subsurface behavior around demersal trawl gear. Using video cameras mounted inside trawl nets, we recorded the subsurface behavior of common bottlenose dolphins (Tursiops truncatus) in a demersal fish trawl fishery in northwestern Australia. Footage from 36 trawls across the fishery was analyzed to determine the extent of dolphin‐gear interactions and the behavior of dolphins inside the nets. Interaction rates were high, with dolphins present inside and outside the nets during 29 and 34 trawls, respectively, and for up to 99% of the trawl duration. The proportion of foraging behaviors exhibited inside the nets was higher than the proportions of traveling and socializing behaviors. Twenty‐nine individuals were identified inside the net, seven of which returned repeatedly within and between trawls and fishing trips, but were observed primarily in the same localized areas in which they were first recorded. Our results suggest that entering trawl nets may be a frequently occurring, yet specialized behavior exhibited by a small subset of trawler‐associated dolphins. We propose that gear modifications, not spatial or temporal adjustments to fishing effort, have the greatest potential to reduce dolphin bycatch.     

Entanglement‐scar acquisition rates and scar frequency for Bering‐Chukchi‐Beaufort Seas bowhead whales using aerial photography

The Bering‐Chukchi‐Beaufort Seas (BCBS) bowhead whale (Balaena mysticetus) has been considered at low‐risk for entanglement injuries and ship strikes because their range is mainly north of commercial fisheries; nevertheless, changes to their arctic habitat, including a longer open water period and declining sea ice, have resulted in increasing commercial activity and concern about fisheries interactions. We examined interyear matches (between 1985 and 2011) from a photo identification project and identified whales that had acquired entanglement injuries. We estimated the probability of a bowhead acquiring an entanglement injury using two statistical methods: interval censored survival analysis and a simple binomial model. Both methods give similar results, suggesting a 2.2% (95% CI: 1.1%–3.3%) annual probability of acquiring a scar. We also include an entanglement scar frequency analysis of aerial photographs from the 2011 spring and fall surveys near Point Barrow, Alaska, which suggest 12.4% of live bowheads show evidence of entanglement scarring. Entanglement rates for the BCBS bowhead stock are lower than many other large whale stocks, and abundance has increased over the past 35 yr; however, our findings indicate that fishing gear entanglement is a more serious concern for the BCBS bowhead whale population than previously thought.     

Arctic marine fishes and their fisheries in light of global change

In light of ocean warming and loss of Arctic sea ice, harvested marine fishes of boreal origin (and their fisheries) move poleward into yet unexploited parts of the Arctic seas. Industrial fisheries, already in place on many Arctic shelves, will radically affect the local fish species as they turn up as unprecedented bycatch. Arctic marine fishes are indispensable to ecosystem structuring and functioning, but they are still beyond credible assessment due to lack of basic biological data. The time for conservation actions is now, and precautionary management practices by the Arctic coastal states are needed to mitigate the impact of industrial fisheries in Arctic waters. We outline four possible conservation actions: scientific credibility, ‘green technology’, legitimate management and overarching coordination.     

Gear modifications reduced humpback whale entanglements in a commercial rock lobster fishery

Entanglement of whales in fishing gear occurs globally and where populations are recovering from past exploitation, entanglement frequency is likely to increase. The Western Australian population of humpback whales (Megaptera novaeangliae) is growing rapidly, yet from 1990 to 2010 the number of whales reported entangled in gear from the pot-based western rock lobster fishery was relatively stable at around one per year. However, from 2010, reported entanglements increased, reaching a maximum of 17 in 2013. This increase occurred immediately after a shift to a year-round quota-based fishery that eliminated the annual 4½-month closure that coincided with the whale migration. Gear modifications that eliminated surface rope, shortened rope lengths, and reduced float numbers were implemented in June 2014 to reduce whale entanglements. The effectiveness of these modifications was evaluated using a Bayesian model that incorporated changes in humpback whale population size, entanglement reporting probability, fishing effort, and whale migration timing. Our analyses indicate that gear modifications reduced entanglement in fishing gear from the rock lobster fishery by at least 25% (with 95% probability), with a median reduction of 64%. The model also showed that the greatest entanglement risk occurs on the northward migration and in water depths of 55–73 m.     

Estimating the success of protected areas for the vaquita,Phocoena sinus

Bycatch in artisanal gill nets threatens the vaquita, Phocoena sinus, with extinction. In 2008 the Mexican government announced a conservation action plan for this porpoise, with three options for a protected area closed to gill net fishing. The probability of success of each of the three options was estimated with a Bayesian population model, where success was defined as an increase in vaquita abundance after 10 yr. The model was fitted to data on abundance, bycatch, and fishing effort, although data were sparse and imprecise. Under the first protected area option, the existing Refuge Area for the Protection of the Vaquita, bycatch was about 7% of population size, and probability of success was 0.08. Under the second option with a larger protected area, the probability of success was 0.35. The third option was large enough to eliminate vaquita bycatch and had a probability of success >0.99. Probability of success was reduced if elimination of vaquita bycatch was delayed or incomplete. Despite considerable efforts by the Mexican government to support vaquita conservation, abundance will probably continue to decline unless additional measures to reduce vaquita bycatch are taken, such as banning gill nets within the vaquita's range and developing effective alternative fishing gear.     

Genetic divergence over small geographic scales and conservation implications for Commerson's dolphins (Cephalorhynchus commersonii) in southern Argentina

Cephalorhynchus commersonii is distributed in the nearshore coastal waters of South America, and thus is particularly vulnerable to bycatch in coastal nets and trawls. Our study documents genetic structure in presumed Commerson's dolphin subpopulations along the southern Argentina coastline, from the Ría Deseado in the north to Ría Gallegos in the south, and focuses on the potential for depletion in the apparently more heavily impacted Ría Gallegos area. Only two control region (423 bp) haplotypes were shared among all these locations (out of 11 identified), and striking differences in haplotype frequencies between areas are apparent. AMOVA analysis, using mitochondrial sequence data, indicates significant population subdivision (overall F_ST= 0.21, P < 0.001) between Ría Deseado (n= 8), Bahía San Julián (n= 11), Ría Gallegos (n= 31), and a small sample of dolphins from the captive colony at San Diego Seaworld (n= 7) derived from animals originally captured in the Strait of Magellan. Comparisons based on haplotypic distances indicated relatively strong differences between regions (Φ_ST= 0.30, P < 0.001). This research provides the first indication of reduced gene flow and genetic differentiation within local subpopulations of Commerson's dolphins, along a relatively small stretch of coastline.     

Blood Biochemistry of Sea Turtles Captured in Gillnets in the Lower Cape Fear River,North Carolina,USA

ABSTRACT Mortality due to fisheries interactions has been implicated as a contributor to population decline for several species of sea turtle. The incidental capture of sea turtles in the coastal gillnet fisheries of North Carolina, USA, has received much attention in recent years, and mitigation measures to reduce sea turtle mortality due to gillnet entanglement are a high priority for managers and conservationists. Efforts to evaluate effects of gillnet entanglement on sea turtle populations are complicated by the lack of information on health status of turtles released alive from nets and postrelease mortality. We obtained blood samples from green (Chelonia mydas) and Kemp's ridley (Lepidochelys kempii) sea turtles captured in gillnets for 20–240 minutes to assess the impacts of gillnet entanglement on blood biochemistry and physiological status. We measured concentrations of lactate, corticosterone, ions (Na⁺, K⁺, Cl^-, P, Ca²⁺), enzymes (lactate dehydrogenase [LDH], creatine phosphokinase [CPK], aspartate aminotransferase [AST]), protein, and glucose in the blood and also performed physical examinations of turtles to document external indicators of health status (injuries, lethargy, muted reflexes). We evaluated the effects of entanglement time on blood biochemistry and to look for correlations between blood biochemistry and results of the physical examinations. We observed a significant increase in blood lactate, LDH, CPK, phosphorus, and glucose with increased entanglement time. Alterations in blood biochemistry were generally associated with a decline in health status as indicated by results of the physical examination. Although entanglement time plays an important role in determining the health status of sea turtles upon release from a gillnet, our results suggest that factors such as the depth and severity of entanglement may also have an effect on health status of turtles and the probability of postrelease survival. We were unable to set a maximum unattended gillnet soak time to minimize impacts on captured sea turtles, and therefore recommend that fisheries managers continue to enforce the net attendance regulations currently in place in the lower Cape Fear River, North Carolina, during the summer months.     

Assessing changes in numbers and distribution of large whale entanglements in Newfoundland and Labrador,Canada1

Entanglements of large whales in commercial fisheries in Newfoundland and Labrador, Canada, have been consistently recorded since 1979, as part of a program aimed at releasing captured animals and reducing costs to fishermen. This data set represented an opportunity to identify fisheries posing particular entanglement risks to local whale populations. Data were assessed over the periods 1979–1992 and 1993–2008, corresponding to distinct phases in fisheries distribution and intensity. Between 1979 and 2008, 1,209 large whale entanglements were recorded in Newfoundland and Labrador. These were mostly humpback whales (Megaptera novaeangliae; 80%) and minke whales (Balaenoptera acutorostrata; 15%). Dramatic declines in reported inshore whale entanglement rates were observed following the 1992 moratorium on Atlantic cod (Gadus morhua) fisheries. Recently, more entanglements have been reported further offshore, largely due to expansion of fisheries targeting snow crab (Chionoecetes opilio). For all whale species, entanglement rates and associated mortality rates varied considerably in different fishing gear. Fractions of humpback and minke whales found dead in different fishing gear differed substantially, with minke whales far more likely to be found dead than humpback whales.