Spatiotemporal variability in northern shrimp (Pandalus borealis) life-history traits in Newfoundland and Labrador

Beita Jiménez, Andrés (2021) Spatiotemporal variability in northern shrimp (Pandalus borealis) life-history traits in Newfoundland and Labrador. Masters thesis, Memorial University of Newfoundland.

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Abstract

After the collapse of the groundfish stocks in the mid-90’s, northern shrimp has become one of the most economically important fisheries in Newfoundland and Labrador. However, the biomass has drastically decline since 2006 to reach similar low biomass levels as before the mid-90’s. Several reasons have been proposed for that decline including the recovery of predators, high fishing pressure, and changes in water temperature. Collapses and slow recoveries of fisheries have often been associated with life-history changes, but this has not yet been documented for northern shrimp in Newfoundland and Labrador. The goal of this thesis is to determine if there is variability in life-histories of northern shrimp and if it has contributed to the observed decline of the stock. I first used data from onboard observers and scientific surveys to estimate variation in size at sex transition from 1995 to 2016 and evaluate which factors are driving this variation. I found that trends in size at sex transition varied depending on the data source, but a general decline was observed. Fishing and temperature were identified as the main factors driving this decline, but the decline is more likely a consequence than a cause of reduction in abundance by fishing. I suggest that a compensatory response to reduced local abundance caused by fishing is the mechanism explaining observed variation in size at sex transition. In the second part of this thesis, I updated estimation of shrimp fecundity, which has not been done for 40 years. Then, I integrated new fecundity estimates with the size structure and size at sex transition information from the previous chapter to test if the variability in life history is affecting the estimation of indices of stock reproductive potential. I found that the number of eggs at size was 30% lower in 2018 than in 1978. However, the variability in size at sex transition and fecundity had little effect on the estimation of stock reproductive potential and did not cause major changes in the categorization of the stock status within the currently precautionary approach. I suggest that for this stock, the spawning stock biomass can be considered a good, parsimonious index to represent the reproductive potential.

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