Availability, usage and expected contribution of potential nursery habitats for the California halibut

Abstract

Coastal ecosystems have been identified as important nursery habitats for many of the world's fishery species. Beyond this, there remain many questions about what exactly constitutes high-value, even critical, habitat for juvenile fish. A first step in investigating nursery habitat value should be to catalogue the spatial coverage (availability) of all potential nursery habitats as well as the distribution (usage) of juvenile fish within those habitats. We conducted two years of fall surveys in the nearshore areas of San Diego County, CA, examining the spatial distribution of 0-group California halibut, Paralichthys californicus. The database generated by 527 otter trawls and block-net seine collections was used to produce a series of models employing regression trees to study the abiotic factors (water column and bottom features) that affect juvenile distributions. Along the exposed coast, highest 0-group densities (0. ). The spatial coverage of potential nursery habitats was calculated using a Geographic Information System (GIS) database, and the total number of resident 0-group halibut within each site was estimated (habitat area  juvenile halibut density) as a proxy for expected contribution of halibut advancing to the adult stock from each nursery. Although 85% of the potential nursery habitat area occurred along the exposed coastline, 69% (2003) to 58% (2004) of 0-group halibut resided in protected embayments. Embayment contribution is much greater in the southern half of the study region, largely due to Mission and San Diego bays. We conclude that all nursery habitat types demonstrate the potential to contribute significantly to stock fitness, and that in general, shallow and better-protected habitats are highly utilized nurseries for 0-group halibut and deserve special attention in management or conservation efforts.

Using Movements and Habitat Utilization as a Functional Metric of Restoration for Estuarine Juvenile Fish Habitat

“…Juvenile California Halibut are thought to use seasonally warm, prey-abundant estuaries to maximize their growth and survival before recruiting to adult stocks (Allen et al 2006;Fodrie and Mendoza 2006;Fodrie and Levin 2008). Halibut typically reach reproductive maturity at 59 cm for females and 32 cm for males, which means that the majority of the fish in our study were likely juveniles (Love and Brooks 1990).…”

“…Because microhabitat conditions (submerged aquatic vegetation, intertidal mudflats, and emergent vegetation) allow estuaries to host juvenile fish at higher densities and increase their feeding and growth potential per unit area, these habitats are better suited to support specific fishery stocks than are exposed coastlines (Irlandi and Crawford 1997;Allen et al 2006;Fodrie and Mendoza 2006).…”

“…California Halibut are a commercially and recreationally important ambush predator species in California (Love 2011). Temperature, depth, water flow, and salinity all influence their spatial distribution in estuaries (Madon 2002(Madon , 2008Fodrie and Mendoza 2006); however, point-of-capture data provide little insight into how these factors affect their short-and long-term habitat use. Therefore, we set out to integrate a traditional monitoring plan using different point-of-capture techniques with a short series of active tracks to elucidate behaviors that might shape habitat selection and connectivity between microhabitats.…”

Tracking juvenile fish movement and nursery contribution within arid coastal embayments via otolith microchemistry

“…Halibut recruit to estuaries at 10 to 70 mm standard length (SL) and begin to emigrate at around 140 mm SL (Kramer 1991). In smaller embayments (< 0.25 km 2 ), abundance is highest near the mouth, while in larger systems (> 0.25 km 2 ), it tends to be highest toward the middle or inner reaches (Fodrie & Mendoza 2006, López-Rasgado 2006. Kramer (1991) found that juvenile halibut within embayments tend to move deeper with age, regardless of distance from the embayment mouth.…”

“…we chemically defined all potential nurseries). North and south of our Baja sites, the coastline is rocky, highly exposed and unsuitable for juvenile halibut (Fodrie & Mendoza 2006). Also, a recent year-long survey found that the nearest sandy shoreline in the region (ca.…”