No abstract

Changes in Arctic fish assemblages resulting from climate change will likely be determined by the differential thermal response of key species during their early life history. In this study, we incubated multiple batches of eggs and larvae of two ecologically important gadids co-occurring at the Pacific–Arctic interface, Arctic cod (Boreogadus saida) and walleye pollock (Gadus chalcogrammus). Fertilized egg batches (n = 11 Arctic cod; n = 6 walleye pollock) were collected in the late winter/early spring from laboratory broodstock held under simulated seasonal environmental conditions. Image and lipid analyses indicated that Arctic cod eggs and larvae were ∼25–35% larger than walleye pollock and had nearly 3–6× more energetic reserves. Two batches of eggs from each species were incubated in replicated containers (n = 3/batch/temperature) at −0.4, 1.2, 2.5, 3.8, 5.0, 9.0, and 12.0°C for Arctic cod and −0.8, 0.3, 2.2, 4.5, 9.0, and 12.0°C for walleye pollock. Both species had very similar low thermal tolerance, but Arctic cod were much more sensitive to higher thermal stress in terms of hatch success and size-at-hatch. For example, Arctic cod hatch success declined precipitously at temperatures above 3.5°C yet remained above 50% in walleye pollock at 9°C. Arctic cod also had significantly longer development times, such that embryos could survive for ∼4 months at temperatures <0°C from the time of spawning to first-feeding. Collectively, these results indicate Arctic cod have a much smaller thermal window for survival, but can survive for longer periods in the absence of food than walleye pollock at cold temperatures. These temperature-dependent rates will be useful in the development of population forecasts and biophysical transport models for these species in the northern Bering, Chukchi, and Beaufort seas.

Little is known regarding bias attributable to fish behavior for visual transects conducted using underwater vehicles (UVs). Experiments were conducted under 2 ambient illuminations to assess the behavioral responses of 7 north Pacific Ocean groundfish species to a light stimulus that simulated the approach of a UV. Species included sablefish Anoplopoma fimbria, Pacific halibut Hippoglossus stenolepis, lingcod Ophiodon elongatus and 4 species in the genus Sebastes: blue rockfish S. mystinus, black rockfish S. melanops, copper rockfish S. caurinus and quillback rockfish S. maliger. Movement, as well as general activity, varied greatly between species. The most active species, sablefish, became agitated and moved away from the looming light source, while the least active species, Pacific halibut and lingcod, typically remained stationary. Of the 4 rockfish species, 2 demonstrated a strong response to ambient light level. Black rockfish and blue rockfish moved away from the looming light source, but avoidance was delayed under high ambient light. Bias probably differs among species, being greatest for those that are highly active and mobile, like sablefish. Further, ambient light may modulate bias, such that researchers need to be cautious about comparing results for surveys conducted at different depths and/or times of day. KEY WORDS: Fish behavior · Light response · Survey bias · Gear avoidance · ROV · Submersible Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 391: [97][98][99][100][101][102][103][104][105][106] 2009 Due to the efficiency of sound propagation in water, fish will probably first detect the sound generated by an approaching UV. Most fish have hearing in the range of 300 to 1000 Hz (Popper 2003), and both electric and hydraulic thrusters probably emit sound in this frequency range. Gadids and herring respond to approaching surface vessels with both diving and horizontal movements (Vabø et al. 2002, Handegard et al. 2003, Handegard & Thøstheim 2005. Similarly, fish may elicit avoidance behavior in response to the noise generated by trawl warps and doors (Handegard & Thøstheim 2005).Artificial lighting also constitutes a major stimulus likely to influence fish; nearly all UVs use lights for video and still photography. As an object or light approaches, the projected image on the observer's retina expands, a process referred to as visual looming (Schiff et al. 1962), which frequently triggers avoidance behaviors in animals. In the ecological literature, this has been applied in the context of predator-prey interactions, and has been used to examine factors such as perception of predator size and prey-reactive distances (Domenici 2002, Paglianti & Domenici 2006. As a UV approaches, the lights from the vehicle will appear to loom to a fish, and as with trawls (Ryer 2008), may be interpreted by the fish as a threat, resulting in avoidance behavior. Alternatively, under some conditions fish are attracted to underwater lights. We frequently use dr...