Longitudinal Growth Differences and the Influence of Diet Quality on Atka Mackerel of the Aleutian Islands, Alaska: Using a Bioenergetics Model to Explore Underlying Mechanisms

Abstract

Atka mackerel Pleurogrammus monopterygius make up the single largest biomass of groundfish in the Aleutian Islands, Alaska, and are an important component of this marine ecosystem. Atka mackerel show a significant decrease in size from east to west. We compared fish from two study areas reflecting this size cline: Seguam Pass in the eastern Aleutians and Amchitka Island in the western Aleutians. At any given age, the Atka mackerel at the former location are larger than those at the latter (e.g., 5‐year‐old fish average 732 g and 39 cm fork length at Seguam Pass but only 575 g and 36 cm at Amchitka Island). Our objectives were to determine the mechanisms underlying the observed differences in growth, such as prey availability, prey quality, and thermal experience. We used a bioenergetics model to examine the effects of diet and temperature on growth. The model estimates of consumption fell within the range of those observed for Atka mackerel, suggesting that the model was an appropriate tool for exploring these effects. The results obtained with the model suggest that prey quality is the main factor in the observed size differences. At Seguam Pass Atka mackerel ate a more energetically rich diet consisting of euphausiids and fish, whereas at Amchitka Island copepods dominated the diet and there was little to no fish consumption. The model results also suggest that thermal experience contributed less to the observed differences in growth than did the composition of the diet. Understanding the mechanisms underlying the growth of Atka mackerel will improve predictions of biomass and yield within the framework of a dynamic ecosystem and a changing climate.

Effects of Maternal Growth on Fecundity and Egg Quality of Wild and Captive Atka Mackerel

“…These results might reflect differences in environmental conditions between these areas. Seguam Pass has been shown to provide better quality food for Atka mackerel than Amchitka Island (Rand 2007). Lower overall growth rates at Amchitka and lower weight at length seem to further support the hypothesis that fish there have less energy available for growth and reproduction once they reach adult sizes.…”

“…The captive fish in this study were generally fed to satiation three times per week. In wild fish, food consumption peaks in the summer but declines by October, when the majority of stomach samples are empty (Rand 2007). Rand (2007) found that the fish at Amchitka Island generally consume less food and lower-quality food than those at Seguam Pass and linked the growth rates observed in those areas to food consumption.…”

“…In wild fish, food consumption peaks in the summer but declines by October, when the majority of stomach samples are empty (Rand 2007). Rand (2007) found that the fish at Amchitka Island generally consume less food and lower-quality food than those at Seguam Pass and linked the growth rates observed in those areas to food consumption. It can be argued, then, that the captive fish's dramatically increased growth rates and increased weight at length are also due to greater food consumption.…”

Higher Aggregation of Key Prey Species Associated with Diet and Abundance of the Steller Sea Lion Eumetopias jubatus across the Aleutian Islands

“…Indeed, Rand et al. () found large differences in the diets of Atka Mackerel in the eastern Aleutian Islands (NMFS Area 541) relative to those in the western Aleutian Islands (Figure ; NMFS Area 542), with the former consuming more energetically rich prey. The diel patterns described in the present study should be explored further with respect to Atka Mackerel prey fields across the Aleutian Islands archipelago.…”

Geographical expansion of Northeast Atlantic mackerel (Scomber scombrus) in the Nordic Seas from 2007 to 2016 was primarily driven by stock size and constrained by low temperatures

“…Temporal variation in prey quality, i.e. energy content, could also contribute (Rand et al, 2010). Mackerel prey on a wide size range of prey items (Prokopchuk and Sentyabov, 2006;Langøy et al, 2012;Óskarsson et al, 2016;Bachiller, et al, 2016) of which the larger prey is poorly sampled with WP2-nets (Gjøsaeter et al, 2000).…”