Larval distribution of offshore spawning flatfish in the Gulf of Alaska: potential transport pathways and enhanced onshore transport during ENSO events

Abstract

Offshore and deepwater spawning flatfish species in the Gulf of Alaska, such as arrowtooth flounder Atheresthes stomias and Pacific halibut Hippoglossus stenolepis, have juvenile nurseries that are inshore, in bays or at the mouths of bays. Larvae must emigrate from their spawning areas along the continental slope and outer shelf towards shore, in a direction across the prevailing Alaskan Stream. Using a 20 yr time series of data from ichthyoplankton surveys in the Gulf of Alaska, we examine patterns of variability in larval halibut and flounder distributions that may reflect processes resulting in successful recruitment to nursery areas. Several patterns can be observed in these data. Eggs and the smallest-sized larvae are distributed deep in the water column along the outer shelf and slope. Larger larvae tend to be located in the upper water column and farther inshore over the continental shelf. Larger larvae are also associated with deep-sea valleys and troughs that penetrate the shelf. Thus, these topographic features may serve as transport pathways to juvenile nursery grounds. ENSO (El Niño-Southern Oscillation) conditions and warm-year anomalies are linked to recruitment strength of Pacific halibut. Variability in larval transport as related to ENSO and other conditions that enhance onshore advection may play an important role in the recruitment of flatfishes to their nursery grounds. The results of this analysis indicate that larvae of both species are more abundant in coastal areas during El Niño events, and that a higher proportion of larvae are transported inshore during El Niño years.

Identifying spawning behavior in Pacific halibut, Hippoglossus stenolepis, using electronic tags

“…We propose that the depth of the apex of the spawning rise is a means for the female to vertically position the eggs and the subsequent drifting larvae in the water column. Correct depth selection for egg release may ensure onshore transport into coastal juvenile nursery grounds by the prevailing current (Bailey & Picquelle 2002). Table 1.…”

Fine-scale population genetic structure in Alaskan Pacific halibut (Hippoglossus stenolepis)

“…Many studies have suggested that population structure of benthic marine fishes is influenced by larval transport dependent on oceanic current systems and wind patterns (Parker 1989;Koutsikopoulos et al 1991;Nielsen et al 1998;Stepien 1999;Bailey and Picquelle 2002;Wilderbuer et al 2002;Knutsen et al 2007). Benthic species can experience genetic homogenization as a consequence of mixing during the transport of pelagic eggs and larvae despite geographically distinct spawning locations (Hauser et al 2006;Rooper et al 2006;Bailey et al 2008).…”

Subtle genetic population structure in Pacific halibut Hippoglossus stenolepis

“…Adult H. stenolepis are highly migratory, with some individuals moving hundreds of km over several months (Seitz et al ., ; Webster et al ., ). In addition, H. stenolepis have a long pelagic larval phase in the order of 6 months (St Pierre, ), in which they are dispersed by ocean currents that could result in long‐distance connectivity among populations (Thompson & Van Cleve, ; Skud, ; Bailey & Picquelle, ). Despite the plethora of evidence supporting extensive movement of H. stenolepis , little is known about gene flow among populations.…”