Inter-Annual Distributions of Larval and Pelagic Juvenile Cod ( Gadus morhua ) in Southwestern Nova Scotia determined with two Different Gear Types
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 limitation...
| Published in: | Canadian Journal of Fisheries and Aquatic Sciences |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Canadian Science Publishing
1989
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1139/f89-076 http://www.nrcresearchpress.com/doi/pdf/10.1139/f89-076 |
| Summary: | 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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