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Sitka, AK, United States

Sreenivasan A.,Sitka Sound Science Center | Heintz R.,National Oceanic and Atmospheric Administration
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2016

Pacific cod (Gadus macrocephalus) are generalist predators in the Gulf of Alaska (GOA), and are an important predator on other commercially important species. Efficient management of this species can benefit by knowing how these fish adapt to changing environmental conditions, with a focus on how growth and condition are affected by changes in temperature and diet. We conducted a feeding study to understand the relationship between growth, ration, and temperature, and how these factors interact to affect energy allocation strategies. Since growth and condition of juveniles can determine recruitment into the population, this study focused on growth and consumption of age 1+Pacific cod held over 4 temperature treatments (4. °C, 8. °C, 12. °C, and 16. °C) and 3 ration levels (unlimited ration, medium ration, and low ration). We also compared cellular nucleic acid (RNA/DNA) ratios, an instantaneous growth index, total-body lipid, and proximate composition between fish. At 4. °C, 8. °C, and 12. °C, fish at medium and low rations had higher growth rates relative to fish at high rations. Higher food consumption appears to negatively affect digestive ability, assimilation efficiency, and nutrient utilization. RNA/DNA was clearly correlated with growth rates at 4. °C and 8. °C, but this relationship did not hold at higher temperatures. A secondary growth study was conducted to test the reliability of the growth/consumption models derived from the main growth study. Temperature influenced energy reserves (lipid) while tissue growth (protein) was influenced by ration level. Average lipid values were higher at 4. °C than at 8. °C or 12. °C, suggesting a predisposition to heightened lipid synthesis at colder temperatures. Longer durations of warmer water temperature in the GOA could consequently affect energy allocation strategies, with dietary changes in the field potentially amplifying this effect in cold and warm years. This energy allocation strategy could be detrimental with warmer temperatures predicted in the GOA. © 2016 Elsevier Ltd.

O'Connell V.,Sitka Sound Science Center | Straley J.,University of Alaska Southeast | Liddle J.,University of Alaska Southeast | Wild L.,Sitka Sound Science Center | Thode A.,University of California at San Diego
ICES Journal of Marine Science | Year: 2015

In Alaska, sperm whale (Physeter macrocephalus) depredation on longline sets has increased since implementation of the Individual Fishing Quota programme in 1995. A collaborative effort (SEASWAP) between longliners, scientists, and managers has undertaken research to evaluate this depredation with a primary objective to develop and test a passive deterrent that would reduce depredation without reducing catch rate of sablefish (Anoplopoma fimbria). Commercial longliners, fishing for their own sablefish quotas during the regular season, deployed beaded gear (25 mm lucite beads attached to gangions) with control gear and set recorders to collect acoustic data. Beaded and control gear were randomly assigned by skate quad (672 hooks) with 5 quads in each longline set. Acoustic recorders were used to document sperm whale creak-pause events, representative of depredation of the longline gear. Although there were more sablefish per skate quad on the beaded gear and there was a decrease in depredation events on the beaded gear compared with the control, neither effect was significant (p = 0.205 and 0.364, respectively). The SEASWAP project is testing other deterrent strategies including gear modifications and the establishment of a sighting network to improve avoidance. © 2015 International Council for the Exploration of the Sea 2015. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Straley J.,University of Alaska Southeast | O'Connell V.,Sitka Sound Science Center | Liddle J.,University of Alaska Southeast | Thode A.,University of California | And 4 more authors.
ICES Journal of Marine Science | Year: 2015

In Alaskan waters, depredation on sablefish longline gear by sperm whales increases harvesting cost, negatively biases stock assessments, and presents a risk of entanglement for whales. The Southeast Alaska Sperm Whale Avoidance Project (SEASWAP), a collaborative effort involving industry, scientists, and managers, since 2003 has undertaken research to evaluate depredation with a goal of recommending measures to reduce interactions. Prior to 2003, little was known about sperm whale distribution and behaviour in the Gulf of Alaska (GOA). Although fishers were reporting increasing interactions, the level of depredation varied with no apparent predictor of occurrence across vessels. Between 2003 and 2007, fishers were provided with fishery logbooks and recorded information on whale behaviour, whale presence and absence, during the set, soak, and haul for 319 sets in the GOA. Data were evaluated for a vessel, area, and seasonal (month) effect in the presence and absence of sperm whales. Using catch per unit effort (cpue) as a metric, in kg/100 hooks, results indicated that depredation depended on both the vessel and the area. More whales associated with vessels from April to August. Sperm whales were also likely to be present when cpue was high, revealing that whales and fishers both knew the most productive fishing areas, but confounding the use of cpue as a metric for depredation. Using a Bayesian mark-recapture analysis and the sightings histories of photo-identified whales, an estimated N=135 (95% CI 124, 153) sperm whales were associating with vessels in 2014. A spatial model was fitted to 319 longline sets and quantified a 3% loss in cpue, comparable to other global studies on sperm whale depredation. Through all phases of SEASWAP, our understanding of depredation has gained significantly. This successful collaboration should be considered as a model to create partnerships and build collaborations between researchers and fisherpeople encountering marine mammal interactions with fishing gear. © 2015 International Council for the Exploration of the Sea 2015. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Thode A.,University of California at San Diego | Mathias D.,University of California at San Diego | Straley J.,University of Alaska Southeast | O'Connell V.,Sitka Sound Science Center | And 6 more authors.
ICES Journal of Marine Science | Year: 2015

Since 2003, a collaborative effort (SEASWAP) between fishers, scientists, and managers has researched how Alaskan sperm whales locate demersal longline fishing activity and then depredate sablefish from gear. Sperm whales constantly produce relatively low-frequency biosonar signals whenever foraging; therefore, over the past decade, passive acoustic monitoring (PAM) has become a basic tool, used for both measuring depredation activity and accelerating field tests of potential depredation countermeasures. This paper reviews and summarizes past published PAM research on SEASWAP, and then provides a detailed example of how PAM methods are currently being used to test countermeasures. The review covers two major research thrusts: (i) identifying acoustic outputs of fishing vessels that provide long-distance "cues" that attract whales to fishing activity; and (ii) validating whether distinctive "creak" sounds can be used to quantify and measure depredation rates, using both bioacoustic tags and statistical comparisons between visual and acoustic depredation estimates during federal sablefish surveys. The latter part of the paper then provides an example of how PAM is being used to study a particular potential countermeasure: an "acoustic decoy" which transmits fishing vessel acoustic cues to attract animals away from true fishing activity. The results of an initial 2011 field trial are presented to show how PAM was used to design the decoy signals and monitor the efficacy of the deployment. The ability of PAM to detect both whale presence and depredation behaviour has reduced the need to deploy researchers or other specialists on fishing cruises. Instead, volunteer fishers can deploy "user-friendly" acoustic recorders on their gear, greatly facilitating the testing of various deterrents, and providing the industry and regulators a convenient and unobtrusive tool for monitoring both the scale and long-term spread of this behaviour across the Alaskan fishery. © 2015 International Council for the Exploration of the Sea 2015. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

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