Interactions between climate and population density in the episodic recruitment of bocaccio, Sebastes paucispinis, a Pacific rockfish

Abstract

Climate strongly influences the population dynamics of many species, but intrinsic and extrinsic factors such as density-dependence and anthropogenic impacts can confound the effects of climate. Further, the temporal scale of climate response is determined by the unique characteristics of a species' life history, and determining the most appropriate climate indicator at the proper scale is a challenge faced by population ecologists. We focused on how climate influences juvenile survival of bocaccio (Sebastes paucispinis), a threatened Pacific rockfish, because its abundance has declined >90% in the last 25 years, ostensibly as the result of overfishing. Bocaccio recruitment is episodic, with strong recruitment events apparently related to climate conditions. We developed a sequence of models that related log of juvenile survival to the predictor variables population density and climate, as measured by the Northern Oscillation Index. A model that contained only population density as a predictor variable explained only 1.4% of the variance, while a model that included only climate indices explained 52%. Including density additively with climate did not improve model fit. However, a model that included an interaction between density and climate explained more than 68% of the variance. In addition, models that represented climate as monthly indices fit the juvenile survival data much better than those that averaged climate over 2-or 3-month periods. Our results suggest that climate affects bocaccio recruitment as a series of pulses corresponding to particular life-history events, with population density mediating the magnitude of the climate effect during the settlement stage.

Larvae define spawning habitat of bocaccio rockfish Sebastes paucispinis within and around a large southern California marine reserve

“…The idea that larval survival was relatively high in 2004 was supported by the fact that bocaccio recruitment success (number of recruits per spawners) was much greater in than in 2002or 2003(Zabel et al 2011. Additionally, when recruitment success was modeled against environmental variability, success was greater in 2004 than the model predicted (Zabel et al 2011). Although our study was not explicitly designed to test the effect of the CCA on bocaccio production, these results suggest that cessation of fishing-induced mortality may have resulted in an increased larval output/survival within its bounds 3 yr after it was established.…”

“…Hence, the cessation of fishing-induced mortality may have eased the elimination of larger, older fish, and had a positive effect on both larval output and quality (Pope 2009, Ralston & MacFarlane 2010) in a year with favorable environmental conditions. The idea that larval survival was relatively high in 2004 was supported by the fact that bocaccio recruitment success (number of recruits per spawners) was much greater in than in 2002or 2003(Zabel et al 2011. Additionally, when recruitment success was modeled against environmental variability, success was greater in 2004 than the model predicted (Zabel et al 2011).…”

“…After parturition, larval bocaccio are approximately 4.0 to 5.0 mm long (Moser 1996), and typically occur in the upper 100 m of the water column (Ahlstrom 1959, Lenarz et al 1991, Ross & Larson 2003. Juveniles usually settle to demersal, nearshore rocky areas by 3.5 mo, before gradually moving to deeper, offshore habitats (Love et al 2002, Tolimieri & Levin 2005, Zabel et al 2011. Adults are found to depths of approximately 500 m but are most common between 50 and 250 m where they associate with complex rocky reef substrate (Love et al 2002).…”

“…We also measured 4 environmental parameters (sea surface temperature, chlorophyll a, depth, and ocean currents) that previous studies suggest impact rockfish during their pelagic larval phase (Moser et al 2000, Taylor et al 2004, Doyle et al 2009, Zabel et al 2011) and could therefore potentially account for patterns in larval distribution and abundance. Sea surface temperature and depth were recorded concurrently with ichthyoplankton sampling at each station (N = 73).…”

“…may be further impacted by interannual changes due to El Niño events (Bograd & Lynn 2003). Given that sea surface temperature, chlorophyll a, and ocean currents are known to influence bocaccio early life history dynamics (Moser et al 2000, Tolimieri & Levin 2005, Zabel et al 2011, measurement of ocean ographic conditions during larval sampling is necessary to contextualize potential changes in larval presence or abundance. This study presents an analysis of samples collected in 3 consecutive years (2002 to 2004) following the establishment of the CCA to evaluate how variability in oceanographic conditions affected larval dynamics.…”