Interactions of predators, habitat and conspecifics on the coastal distribution of age 0 juvenile cod (Gadus spp.) in Newfoundland
Newly settled age 0 juvenile cod, Atlantic cod Gadus morhua and Greenland cod Gadus ogac, coexist in nearshore areas around Newfoundland, but little is understood on the mechanisms affecting their distribution. In young marine fish, predation risk is often high yet there is generally an increasing c...
| Main Author: | |
|---|---|
| Format: | Thesis |
| Language: | English |
| Published: |
Memorial University of Newfoundland
2003
|
| Subjects: | |
| Online Access: | https://research.library.mun.ca/10855/ https://research.library.mun.ca/10855/1/Laurel_BenjaminJeffrey.pdf |
| Summary: | Newly settled age 0 juvenile cod, Atlantic cod Gadus morhua and Greenland cod Gadus ogac, coexist in nearshore areas around Newfoundland, but little is understood on the mechanisms affecting their distribution. In young marine fish, predation risk is often high yet there is generally an increasing capacity in larger individuals to evade predators. It is therefore difficult to distinguish the role of behaviour and differential survival on distribution of fish in their early life stages. In a series of field and laboratory experiments, I investigate how habitat complexity, predators and conspecific density interact to affect survival and behaviour in juvenile cod, and ultimately, their distribution in coastal Newfoundland. -- In a bay-scale study (~10 km²), I monitored patterns of settlement and distribution of G. morhua and G. ogac, following a large-scale alteration of nearshore eelgrass (Zostera marina) habitat. Comparisons of bi-weekly sampling between control and experimental sites from 1995-2001 indicated a significant increase in cod abundance at sites enhanced with simulated eelgrass and a corresponding decrease in cod numbers at sites where eelgrass had been removed. These data supported predictions, demonstrating that: 1) there was a sufficient supply of juvenile cod within the range of areas that have historically been unoccupied (i.e. sand) and 2) both species preferred to settle in complex habitats. However, G. ogac responded significantly to the removal of eelgrass in more comparisons than G. morhua (70% and 37% respectively), suggesting that G. ogac have a higher affinity for complex vegetative habitats than G. morhua at the scale of manipulation (ca. 800m²). Furthermore, despite an overall preference for eelgrass habitat, high within-site catch variation indicated that individuals of both species were not restricted to any single seine site. Rather, the highly variable data indicate that juvenile cod were mobile and occasionally aggregated throughout the study period. My results support previously ... |
|---|