Latitudinal, ontogenetic, and historical shifts in the diet of a carnivorous teleost, Arripis trutta, in a coastal pelagic ecosystem altered by climate change

Abstract

Changes to the global climate are driving alterations to boundary current-influenced marine ecosystems. The diet of a pelagic teleost, Arripis trutta, was examined in the East Australian Current (EAC)-dominated coastal waters of southeastern (SE) Australia. The diet of A. trutta was dominated by pelagic baitfish, primarily Australian sardine (Sardinops sagax) and scads (Trachurus spp.). Diet varied substantially with both latitude and season linked to variability in the distribution and abundance of key prey species. An ontogenetic diet shift occurred, with crustaceans and polychaetes making up a large proportion of the diet of small fish compared with the dominance of baitfish at larger sizes. The diet of A. trutta has undergone a dramatic shift from one dominated by krill (Nyctiphanes australis) historically to baitfish today. This change is consistent with a well-documented regime shift caused by the increasing intensity of the EAC on coastal SE Australian waters. Understanding the temporal dynamics of this ecosystem is crucial for management of coastal fisheries and also for understanding the impacts of climate change on boundary current-dominated marine ecosystems worldwide.

Top-down pressure on small pelagic fish by eastern Australian salmon Arripis trutta; estimation of daily ration and annual prey consumption using multiple techniques

“…The methods used were: i) experimentally measuring gastric evacuation rates in the laboratory using wild-caught captive fish (Olson and Boggs, 1986;Olson and Mullen, 1986) and then applying this rate to the observed diet of fish sampled in the wild (Hughes et al, 2013); ii) using a bioenergetics model (Fish Bioenergetics 3.0 -The University of Wisconsin) designed to quantify the physiological and ecological constraints to growth and the strength of predator-prey relationships (Hanson et al, 1997;Hartman and Kitchell, 2008); and iii) using an empirical formula derived for multiple regression models for a suite of fishes dependent on shape, size, habitat, temperature and food type Pauly, 1989, 1998). From each technique, it was possible to estimate the amount of food ingested (Q) by a population expressed as a fraction of its biomass (B) per year (Q/B).…”

“…1 Q/B was therefore calculated using each technique at two environmentally relevant temperatures for this region, 15 and 20°C, to provide a plausible range of values. Q was estimated using diet composition presented in Hughes et al (2013). The biomass of the A. trutta stock in SE Australia is estimated to be between 4,500 and 10,000 t (Hughes, 2012).…”

“…The fish were maintained in captivity in a cylindrical (Ø = 496 cm, depth = 159 cm) 35,000 L flowthrough seawater tank with ambient water temperature and photoperiod. Their diet in captivity consisted of a range of small fish, squid and prawns similar to prey found in the stomachs of wild-caught fish (Hughes et al, 2013). Captive A. trutta were fed daily.…”

“…It sustains important commercial fisheries throughout SE Australia, with current landings amongst maturity in 2.2 years at 31 cm FL and a maximum size of 78 cm FL and 7.4 kg (Hartill and Walsh, 2005;Stewart et al, 2011). In combination with observations of the voracious feeding behaviour of A. trutta (Hughes et al, 2013), it is therefore likely that A. trutta require substantial quantities of prey to accommodate their energy requirements for growth and metabolism.…”

“…The lack of knowledge regarding consumption rates on small zooplanktivorous species by large pelagic fish in the temperate waters of SE Australia, coupled with recent concerns over the effects of climate change on this ecosystem (e.g. Hallegraeff, 2010;Hughes et al, 2013;Johnson et al, 2011;McLeod et al, 2012;Poloczanska et al, 2007), initiated interest in better understanding the consumption rates of A. trutta in this region. The objective of this study was therefore to estimate A. trutta predation rates, daily ration and annual prey consumption and examine the potential for the species to exert top-down pressure on small zooplanktivorous fishes in this region.…”