long-term changes in size–depth distributions of urophycis tenuis white hake in the southern gulf of st lawrence and cabot strait

Abstract

the body length–water depth distribution of urophycis tenuis white hake (pisces, gadidae) in the southern gulf of st lawrence (1971–1975, 1981–1985, 1991–1995 and 2001–2002) and cabot strait (1994–1997) was examined. contrary to expectation, linear regression analyses indicated 13 of 17 years had negative slopes with larger fish being found in shallower water. length–depth relationships were statistically significant for five of 17 years (negative slopes: 1971, 1972, 1975, 1981; positive slope: 2002). regression slopes generally increased from 1971 to 2002 indicating the length–depth relationship changed from negative in the early 1970s and 1980s, to negative and positive in the early 1990s, and finally to positive in 2001–2002. in the cabot strait, a significant positive relationship was observed for fish length and water depth indicating large u. tenuis generally occurred in deeper water. we propose that slopes of the length–depth relationship became positive in the 1990s and early 2000s due to the loss of large u. tenuis taken in a seasonal fishery in the southern gulf of st lawrence that targeted highly aggregated spawning and post-spawning shoals of fish in shallow water during summer.

Length–depth relations of Enchelyopus cimbrius fourbeard rockling (Gadiformes: Phycidae) from the southern Gulf of St Lawrence and Cabot Strait in relation to abiotic factors

“…Enchelyopus cimbrius were essentially absent from the Magdalen Shallows and the large central portion of the southern Gulf of St Lawrence which were dominated by sand and gravel substrates. The distribution we report for E. cimbrius is comparable to that of Urophycis tenuis white hake, another gadid typically found on mud substrates (Collette & Klein-McPhee, 2002) with a bimodal shallow-water–deep-water distribution in the southern Gulf of St Lawrence (Benoît et al , 2003; Herder et al , 2005).…”

“…The more limited depth-range sampled in the southern Gulf of St Lawrence (13 -386 m) and Cabot Strait (37 -534 m) may therefore contribute to the absence of a positive size -depth relationship for this species given that 650 m is considered the maximum depth for E. cimbrius (Cohen & Russo, 1979;Collette & Klein-McPhee, 2002). Herder et al (2005) proposed fishing pressure as an explanation for the positive body size -depth relationship that became increasingly evident over time for Urophycis tenuis as large fish were removed from shallow water spawning sites in the eastern Northumberland Strait of the southern Gulf of St Lawrence. Fishing pressure as an explanation for the lack of a positive body size -depth relationship would not appear to apply to E. cimbrius unless considerable numbers were taken as bycatch, an unlikely event given that it lives in burrows (Keats & Steele, 1990) and that its small size (,40 cm) and cylindrical body shape should allow it to pass through the mesh of most commercial fishing gears (Scott & Scott, 1988).…”