Seasonal spawning and wind‐regulated retention‐dispersal of early life stage Atlantic cod (Gadus morhua) in a Newfoundland fjord

Abstract

Sequential ichthyoplankton surveys were used to determine the spatial and temporal distribution of eggs and larvae over coastal spawning grounds of Atlantic cod (Gadus morhua) in Smith Sound, Trinity Bay, Newfoundland, during the spring and summer of 2006 and 2007. Egg densities showed similar patterns for both years with two peaks in abundance in spring (March-April) and late summer (late July). A clear progression of development stages (1-4) was observed in spring and summer in 2006 and summer in 2007, suggesting retention of eggs within the Sound during these periods. Modelled predictions of vertical egg distributions indicated eggs were broadly distributed near the surface during spring (March-April), but were concentrated below the pycnocline (>10 m) within the inner portions of the Sound during the summer months (July-August). Back-calculated peaks in spawning based on water temperatures were estimated at 11 and 4 April for 2006 and 2007, respectfully, with late season peaks centred on 21-24 July for both years. Environmental data indicated cooler water temperatures and periods of high wind stress in spring, and warmer, calmer periods late summer, consistent with higher retention and faster development times on the spawning grounds later in the season. We conclude that spring and summer spawning events result in different distributions of early life stages and may lead to different distributions of juvenile and adult fish.

Egg development rates for use in egg production methods (EPMs) and beyond

“…the use of Paulik diagrams utilizing modeled data (Nash, 1998) for Irish Sea plaice, egg drift modeling such as for plaice in the North Sea (van der Veer et al, 1998;Bolle et al, 2009) or Irish Sea (Fox et al, , 2009, haddock in the North Sea (Heath and Gallego, 1998), and cod off Newfoundland (Bradbury et al, 2000). Egg development rates along with particle tracking models and field data have been used to raise hypotheses concerning distribution patterns, mortality rates and retention (Pepin and Helbig, 1997;Bradbury et al, 2001;Knickle and Rose, 2010). Egg development rates have also been used in the determination of spawning or hatch dates ( Van der Veer et al, 2000;Fox et al, 2007) and dispersal patterns of a variety of species (van der Molen et al, 2007).…”

Acoustic markers of Atlantic cod (Gadus morhua) spawning in coastal Newfoundland

“…Locating the place and time of spawning of gadoids has typically been attempted using three methods: (1) analysis of maturation data of specimens captured in research trawling or commercial fisheries (e.g., Hutchings et al, 1993;Jakobsen, 1987;Marteinsdóttir and Björnsson, 1999); (2) ichthyoplankton surveys (e.g., Brander, 1994;Bradbury et al, 2000;Knickle and Rose, 2010); and (3) a combination of acoustic and other methods (e.g., Rose, 1993;Ouellet et al, 1997;Tomkiewicz et al, 1998). Very few studies have simultaneously described distributions of spawning adults and resultant eggs and larvae with resultant links made between the life stages (see Rose et al, 2008).…”

Northern cod comeback

“…The only large aggregation of overwintering and spawning northern cod was located inshore in Smith Sound, a small fjord on the western side of Trinity Bay (Knickle and Rose 2010;Rose et al 2011). At its peak, this aggregation measured about 26 000 t, and unlike the offshore fish, retained a wide length and age distribution and good condition.…”