Testing Non-parametric Methods to Estimate Cod (Gadus morhua) Recruitment in NAFO Divisions 3NO

Recognizing that non-parametric methods to estimate fish stock recruitment are generally simple and they do not need to be based on ecological hypotheses, four non-parametric methods; the probability transition matrix and three algorithms to estimate recruitment probability density functions were tested on cod (Gadus morhua) data from NAFO Div. 3NO. The transition matrix method was inadequate because the cod stock failed to meet the primary Markovian assumption: the transition probability must be constant and depend only on the previous state. Of the three algorithm methods, the fixed-interval, the New England and the Cauchy, only the New England was appropriate for calculating recruitment with these stock data. A regression coefficient of r = 0.556 (d.f. = 23, P = 0.003) was obtained when the observed data were compared with the estimated. The validity of estimates of future recruitment using the New England algorithm depends on biotic and abiotic environmental conditions being similar in both the pre-recruit and the observation periods

Cod Year-class Variations and Abundance of Other Commercial Fish in NAFO Divisions 3NO

Possible biological relationships of cod (Gadus morhua) with other important commercial fishes are explored. Cod year-class variations are compared with variations of yellowtail flounder and American plaice spawning biomass, mackerel age 1+ group abundance, and redfish densities. The adult fish biomass of these species are considered as an index of their egg and larval abundances. Possible competitive and predator-prey relationships between the 0-age groups and young individuals of cod and these species are examined through correlation analyses. No significant relationships between cod and redfish and yellowtail flounder were found. It seems that mackerel is a predator on cod larvae. A positive high correlation between spawning American plaice biomass and cod year-class strength was found. High American plaice spawning biomass may promote high cod recruitment through a predator-prey interaction. Alternatively, both species may respond similarly to an environmental signal

Year-class Variations of American Plaice and Yellowtail Flounder in Div. 3LNO and the Abundance of Other Commercial Fish

In a previous paper (Paz and Larrafieta, 1989) we obtained a significant positive correlation between cod year-class size in Div. 3NO and American plaice spawning biomass in Div. 3LNO, that was interpreted by supposing a strong predation of 0-group cod on 0-group American plaice. On the contrary, we have not found significant correlations between cod year-classes and spawning biomasses of other species in the area as redfish, yellowtail and mackerel. Following the same method, in this paper we explore correlations between American plaice (Hippoglossoides platessoides) and yellowtail flounder (Limanda ferruginea) year-class sizes and biomasses of adult fishes of these species and those of cod (Cactus morhua), mackerel (Scomber seombrus) and redfishes (Sebastes app.

Cod Stock-Recruitment Relationship in NAFO Divisions 3NO

The cod stock-recruitment relationships in NAFO Div. 3NO were studied by the basic Ricker model and modified Ricker model. Although the models do not adjust to the empirical data, inclusion of the American plaice spawning biomass improves the fit. Adding the mackerel adult biomass also improves the model. Including these two variables in the Ricker model explains almost all variation of the cod stock-recruitment relationship in the area. The confidence level of the parameters in the proposed equation were determined by the bootstrap technique, and its accuracy tested. Was realized a simulation study was performed. The response surfaces show the relations between the four variables studied

Year-class variations of American plaice (Hippoglossoides platessoides) and yellowtail flounder (Limanda ferruginea) in the Grand Banks and the abundance of other commercial fish

The present study analyses the relationships between the recruitment of a species and adult populations of other species. The hypothesis is that reproduction products of some species may be food for the first stages of other species. In a previous paper we obtained a significant positive correlation between cod year-class size in NAFO Div. 3NO and Americanplaice spawning biomass in Div. 3LNO. Following the same method in this study, positive and significant correlations between plaice recruitment and yellowtail flounder, mackerel and redfish adult biomass values were found, but not between yellowtail recruitment and adult biomass values of the other species studied. These results agree with the idea that the Americanplaice is an integral component of the Grand Bank ecosystem