Effects of environmental factors on reproductive potential of the Gulf of Maine northern shrimp (Pandalus borealis)

Abstract

The northern shrimp (Pandalus borealis) once supported a significant winter fishery in the Gulf of Maine (GOM). However, the population collapsed in 2012 and a fishery moratorium has been in effect since 2014 due to record low levels of spawning stock biomass and persistent recruitment failure. An important parameter in determining population dynamics, fecundity, has not been evaluated for more than 30 years, during which time the GOM has warmed significantly. In this study, we quantified three reproductive characteristics related to fecundity: potential fecundity (PF, number of viable eggs), relative fecundity (RF, number of viable eggs per gram of body weight), and egg size (ES) for GOM northern shrimp. The results showed that PF was strongly related to body size, while RF was independent of body size. Egg size declined with increasing body size for larger females. Egg size is related to size at larval hatch, suggesting that although larger females produced more eggs, those eggs may produce smaller larvae. In contrast with previous studies, PF and RF were positively correlated with bottom temperature in the relatively warm years of our study. We hypothesize that the positive temperature-fecundity relationship we observed may not reflect a direct effect, but possibly a compensatory response relating to decreased population density during the time period of our study. In addition, the environmental effects we observed may to some extent reflect progression of the inshore migration of females. The information derived in this study can help us have a better understanding of environmental effects on reproductive potential for climatically vulnerable species such as the GOM northern shrimp.

Keywords

• Potential fecundity
• Relative fecundity
• Egg size
• Environmental effects
• Generalized additive mixed models
• Stock-recruitment