Young-of-the-year recruitment does not predict the abundance of older age classes in black rockfish in Barkley Sound, British Columbia, Canada

Recruitment and connectivity are important criteria for designing effective marine protected areas, as coastal fish populations must be sustained by settling juveniles. However, patterns of recruitment are difficult to observe, and adults and juveniles may occupy distinct habitats. We examined patterns of adult black rockfish Sebastes melanops abundance with respect to habitat and spatiotemporal variability in recruitment of young-of-the-year (YOY) to determine how these variables influence population density in and around a rockfish conservation area (RCA). For most year classes, there was no relationship between the density of YOY and the density of 1 yr olds or the density of adults, and instead habitat variables such as topological complexity and the amount of rocky substrate predicted adult black rockfish abundance. For 1 year class of moderate abundance at the YOY stage but high abundance at the 1 yr old stage, a significant relationship between 1 yr olds and subsequent adults was observed. We surmise that overwinter survival of YOY fish may be an important determinant for year-class strength in black rockfish. Although a companion study found low recruitment of YOY inside the RCA, our data indicate that the density of many species of rockfish was higher inside the RCA. These results highlight how the density of adults can be determined by post-recruitment processes such as movement into suitable habitat and mortality, rather than by recruitment of YOY, and have implications for the design of marine reserve networks.

Assessing the contribution of multiple stressors affecting small-bodied fish populations through a gradient of agricultural inputs in northwestern New Brunswick, Canada

Non-point source discharges, such as agricultural runoff, are often complex mixtures of chemical and non-chemical stressors. The complexity of runoff is compounded by its sporadic releases and few studies have attempted to assess the impacts of runoff on aquatic biota. In this study, an effects based approach was used to examine survival and reproduction of slimy sculpin (Cottus cognatus) in the intensive potato-farming areas of northwestern New Brunswick, Canada. Using non-lethal methods, fish were collected during the ice-free months through a gradient of agricultural intensity. These data were correlated with waterborne levels of pesticides, water temperatures and precipitation data. Results indicate that both adult and young-of-the-year (YOY) fish are longer and heavier in the downstream sites draining areas of higher agricultural intensity. Precipitation has a significant negative relationship with %YOY in the agricultural areas but not in the upstream forested area, indicating that contaminants are present in runoff caused by intensive rainfall events. Our results indicate that YOY sculpin may be at higher risk in the agricultural areas in years of heavier summer rains where peaks in pesticide levels occur. This study expands the existing knowledge base and development of non-lethal methods to define cause–effect relationships.

Hydrological manipulation to assist spawning of a threatened galaxiid fish in a highland lake system

Hydrological alterations threaten freshwater fishes globally, with infrastructure-related modification of inland waterways (e.g. dams, water diversions) having profound impacts on many species. Adapting existing water-management systems can provide opportunities for undertaking hydrological manipulations to assist management of threatened fishes. The present study conducted two hydrological manipulations in an impounded highland lake system in Tasmania, Australia, under differing hydrological conditions in 2007 and 2009, to assist recovery of an endemic species, Galaxias auratus, following a prolonged drought. Monitoring at egg, larvae, juvenile and adult life stages revealed a positive response by G. auratus in Lake Crescent (recipient of water release), with no adverse impact on the species in Lake Sorell (source of water release). In both years, reproductive constraints imposed by water level-related availability of sediment-free rocky substrata delayed spawning (~1 month) of G. auratus in Lake Crescent. Despite this, spawning and recruitment occurred in 2007 (drought year) and 2009 (drought-breaking year), and the 2007 manipulation resulted in a two-fold increase in the seasonal density of larvae in Lake Crescent and an abundant cohort of YOY fish. Given knowledge of life histories and eco-hydrological relationships, manipulating (or re-instating) hydrologic conditions is a powerful tool for assisting recovery of threatened lacustrine fishes.