In¯uence of episodic upwelling on capelin, Mallotus villosus, and Atlantic cod, Gadus morhua, catches in Newfoundland coastal waters D. W. INGS, 1,2 J. K. HORNE, 1,3 AND D. C. SCHNEIDER 1 1 Ocean Sciences Centre, Memorial University of Newfoundland, St John's, Newfoundland, Canada A1B 3X7 2 Corresponding author 3 Present address: Great Lakes Centre, SUNY at Buffalo State College, Buffalo, New York, USA 14222±1095 ABSTRACT Wind-induced upwelling in the north-west Atlantic has been hypothesized to in¯uence catch rates of ®sh by gear ®shing at ®xed locations. Passive movement to shallow depths during upwelling has been proposed to increase encounter rates of ®sh with net leaders set at the coast. However, supporting evidence is not con- clusive, possibly because ®sh respond to strong events rather than all events. We investigated whether catch rates of capelin, Mallotus villosus, and Atlantic cod, Gadus morhua, were related to the strength of upwel- ling, as measured by the rates of water temperature change, or to stage of upwelling. Capelin trap catches were positively related to increases in water tempera- ture, representing the relaxation phase. This result was due primarily to increases in catch after strong (> 4°C change) rather than after typical (< 4°C change) up- welling events. Cod trap catches were not related to upwelling strength but did increase 1±2 days after ty- pical events. The data suggest that upwelling increases capelin movement, while the return of warmer surface water after an upwelling event increases cod move- ment. Key words: upwelling, capelin, cod, catch rates, western Atlantic INTRODUCTION Coastal upwelling is known to alter primary produc- tion, mainly through increases in nutrient supply to the euphotic zone. At upper trophic levels, numerous effects of upwelling have been reported. Changes in distribution and aggregation patterns near upwelling structures have been observed among whales (Smith et al., 1986), marine birds (summarized by Schneider, 1991) and ®sh (Laurs et al., 1977). Foraging patterns and diet compositions of two tuna species are in¯u- enced by upwelling intensity in the California Current (Fiedler and Bernard, 1987). Upwelling frequency has been shown to in¯uence the recruitment of capelin, Mallotus villosus (Leggett and Frank, 1990), and the reproductive success of marine birds (Briggs et al., 1987; Ainley et al., 1995). Effects of coastal upwelling on marine organisms have been examined almost exclusively in eastern boundary current regions, where the direction of the prevailing current favours upwelling. Upwelling also occurs in coastal areas where winds blow contrary to the prevailing current during the passage of storm systems. In the north-west Atlantic, winds from the south-west cause upwelling from late spring to autumn (Sleggs, 1933; Templeman, 1948), despite the pre- vailing southward current. In this system, episodic upwelling is a dominant feature, with short periods of intense upwelling (Frank and Leggett, 1982) super- imposed on the slower rise and fall of the thermocline during the annual cycle. During south-west wind events, cold water from below the seasonal thermo- cline rises to the surface (Leggett et al., 1984) due to longshore wind stress in large bays (Yao, 1987) or cross-shore wind stress in small coves (Taggart and Frank, 1987). The rise and fall of the thermocline can be used to de®ne upwelling and relaxation events in these environments (Schneider and Methven, 1988). Decreases in water temperature of up to 14 degrees over a two-day period occur several times a month (Frank and Leggett, 1982), coincident with the passage of storm systems (Leggett et al., 1984). Changes in the depth of the thermocline can be predicted from models of rate of upwelling (pycnocline rise) due to wind events (Schneider and Methven, 1988). Upwelling of subthermocline water occurs more frequently than strong wind events (Schneider and Methven, 1988) due to propagating internal waves that move the thermocline vertically (deYoung et al., 1993). Biological effects of episodic upwelling in the Labrador Current system have been reported at all Received for publication 20 June 1996 Accepted for publication 11 October 1996 FISHERIES OCEANOGRAPHY Fish. Oceanogr. 6: 1, 41±48, 1997 Ó 1997 Blackwell Science Ltd. 41