Use of rocky intertidal habitats by juvenile pollock Pollachius virens

Abstract

We ~nvestigated patterns of distribution and foraging by young-of-the-year pollock Pollachius virens in the rocky intertidal zone. Pollock were sampled by beach seine in fucoid macroalgae and in open habitats at all stages of the tide, day and night throughout the summer. Their presence in shallow water at the high tidal stages indicated that at least part of the pollock population migrated across the full width of the intertidal zone (150 m) each tide. Densities in shallow water were much higher at low than at high tidal stages suggesting that a large influx of pollock moved in from the subtidal zone at low tidal stages and then dispersed into intertidal habitats at high tidal stages. There were few differences in pollock densit~es between algal and open habitats but abundances likely increased in the algal habitat at higher tidal stages when changes in habitat availability are taken Into account. Densities were higher at night and there was an order of magnitude decline in pollock densities from early to late summer. In another study we showed that piscivorous birds are a probable cause of pollock summer mortality. Pollock fed on invertebrates from intertidal algae relatively continuously. The tidal migrations of juvenile pollock observed in this study and their use of macroalgae as a foraging and possibly a refuging habitat strongly suggests that the rocky intertidal zone may be an important fish nursery area.

Tidal effects on habitat selection and aggregation by juvenile pollock Pollachius virens in the rocky intertidal zone

“…The main seasonal difference was an overall distributional shift towards the subtidal and downshore locations and a preference for greater depths in the intertidal zone. These patterns are consistent with our interpretation of pollock migration when sampled by beach seine (Rangeley & Kramer 1995). In that study, pollock were present in the shallow intertidal zone day and night throughout the summer.…”

“…These findings have important implications for future fisheries and conservation studies; however, obtaining accurate abundance estimates of mobile fishes in the rocky intertidal zone will not be easy. In this study pollock abundance estimates fluctuated widely and were an order of magnitude higher than our beach seine estimates (Rangeley & Kramer 1995) for comparable depths. Despite these difficulties, this study highlights the importance of inferring distribution patterns using more than one method.…”

“…There is evidence that these uses of the rocky intertidal algae also apply to juvenile pollock. Pollock feed on invertebrates associated with fucoid algae but tidal effects may be unimportant as they appeared to forage relatively continuously (Rangeley & Kramer 1995). There is a high potential for predation by piscivorous birds (Rangeley 1994b), and pollock showed a strong refuging response to an experimental presentation of a predator model and to increasing algal habitat availability (Rangeley & Kramer unpubl.).…”

“…They spawn offshore in winter, and the developing eggs and larvae drift in surface waters until spring, when the juveniles (3 to 5 cm in length) migrate inshore (Steele 1963, Scott & Scott 1988, Clay et al 1989. We previously demonstrated that juvenile pollock make extensive use of the intertidal zone (Rangeley & Kramer 1995). Pollock were captured in algae-covered and open patches in similar numbers but foraged primarily on prey from the algal habitat.…”

Riding the tide: estuarine movements of a sciaenid fish, Argyrosomus japonicus

“…The use of tidal rhythms may optimise the foraging success of individuals (Wirjoatmodjo & Pitcher 1984, Szedlmayer & Able 1993, as it enables fish to explore an extensive area with minimal energy expenditure (Rangeley & Kramer 1995, Hartill et al 2003). Due to a higher metabolic rate (Damuth 2001), adopting a strategy that optimises foraging success is particularly important for smaller fish.…”