Spatial variation in distribution, age, and recent growth of postlarval cod (Gadus morhua) were examined off southwestern Nova Scotia during the early summer of 1985 and 1986. Ages ranged between 40–120 d posthatch throughout the sampling area, from the spawning grounds on Browns Bank, to nearshore (<55 m depth) and offshore regions 150 km north. The hatch-date distributions during 1986 between cruises 3 wk apart were significantly different in the nearshore, contrary to the age structure on the Bank which appeared more stable. These observations are consistent with retention of cod in the Browns Bank gyre, coupled with episodic leakage and northerly advection in the residual current. Recent growth determined from otolith increment widths was significantly less for those cod sampled at nearshore stations than for cod offshore and on the Bank. Recent growth was significantly correlated with Zooplankton biomass in a size range suitable for postlarval cod, while sea temperature was correlated in only one cruise. Nearshore areas had on average 25% of the Zooplankton biomass found on the Bank. Recent growth indices of the third and fourth week precapture were not significantly different between the nearshore and offshore, implying that the cod had shared a common environment, and common origin such as Browns Bank.
Strip transect surveys of the large temperate rocky reef fish Cheilodactylus fuscus revealed size-and sex-structured populations across seasons and 3 conditions of wave exposure, from an estuary to the open coast. Large, mostly male, fish (> 30 cm fork length) predominated on the open coast and in deeper water (>10 m), while smaller fish predominated in the more protected estuarine areas and in the subtidal regions (< 5 m), particularly during the winter to spring recruitment period. Aggregations of C. fuscus were geographically persistent, varying in their size and sex composition over 2 yr, which suggested an ontogenetic migration from shallow and protected areas to more exposed coastal locations. Reasons defining the location of aggregations were unclear, as multivariate analysis of 29 habitat characteristics of 13 aggregation sites versus 6 similar control sites revealed no significant difference. Fish re-colonised the same location 2 to 4 mo after a summer and a winter experiment removed > 70% of the adults by intense spear fishing. Experimental sites were recolonised by > 20 cm males and females, and rarely by juveniles. There was no significant difference between the pre-and post-removal estimates of home range of tagged fish at removal sites or in controls.
Ichthyoplankton surveys conducted during 1979 on the Scotian Shelf have shown coincident egg and larval distributions for cod (Gadus morhua) and other related groundfish species. These data have been used by other investigators to support the larval retention hypothesis, in spite of three limitations: the exclusive use of a single type of small sampling gear, limited sampling landward of the 50-m isobath, and analysis of data collected in a single year. During May of 1985, 1986, and 1987 two gear types were used, from the shelf to coastal waters in southwestern Nova Scotia to assess the horizontal distributions of larval and pelagic juvenile cod. Tucker trawl collections made in each year revealed a cohort of cod [Formula: see text] that was not evident in the smaller gear, which effectively sampled cod larvae < 10 mm. During 1985 and 1986, when both larvae and juveniles were abundant, their distributions coincided. The mixture of sizes of cod from 3–45 mm reduced the importance of using multiple gear types. The interannual location of young cod shifted markedly between the nearshore and offshore demonstrating that a single year of sampling effort is inadequate to assess their distribution. Nearshore sampling revealed high densities of young cod as much as three-fold greater than offshore. The inshore waters may serve as a nursery area for young cod originating from offshore spawning sites. Our results confirm the existence of two important sampling limitations of previous cod ichthyoplankton surveys that reduce their utility as empirical support for the retention hypothesis.
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