Effect of oceanographic parameters on daily albacore catches in the Northeast Atlantic

In recent years, albacore (Thunnus alalunga) catches decreased strongly in the Eastern part of the Bay of Biscay. In order to understand the drivers of local albacore catches by fisheries in this area, we analyzed the influence of temperature, salinity and trophic parameters on albacore daily catches by three fleets (baitboat, trolling line and pelagic trawling) traditionally operating in the Bay of Biscay and its surrounding waters. For this, we used oceanographic data obtained from the operational model Regional Ocean Model System (ROMS), for each catch date and location. A Principal Component Analysis performed on these oceanographic data, on Julian day, latitude and longitude, yielded three synthetic variables used as explanatory variables in Generalized Additive Models (GAMs). The first one synthesized most of the variability related to temperature, plankton concentration and longitude. The second one synthesized most of the variability related to surface mixing associated with a seasonal trend. The third one synthesized most of the variability related to salinity and latitude. GAMs revealed a non-linear effect of salinity and latitude on daily catches for all fleets. The effect of mixing was negative for surface gear catches and positive for trawl catches. The trophic and planktonic component had a clear influence only on baitboat and trolling catches. The results are discussed in terms of albacore habitat preferences, vertical distribution and feeding behavior. We suggest that these environmental influences should be considered when using albacore catch data for stock assessment and extrapolating the effects of climate change on albacore abundance in the Bay of Biscay.