System‐Specific Variability in Murray Cod and Golden Perch Maturation and Growth Influences Fisheries Management Options

Abstract

The Murray Cod Maccullochella peelii and Golden Perch Macquaria ambigua are important recreational species in Australia's Murray–Darling Basin (MDB); both species have declined substantially, but recovery is evident in some areas. Minimum length limits (MLLs)—implemented to ensure fish could spawn at least once prior to harvest eligibility—have increased three times in the past decade. We quantified variation in length at 50% maturity (LM50), age at 50% maturity (AM50), and von Bertalanffy growth parameters (k = Brody growth coefficient; L∞ = asymptotic length; t0 = theoretical age at zero length) of these species within two rivers and two reservoirs of the MDB; to investigate whether fish length is a suitable surrogate for AM50 in setting MLLs. Between 2006 and 2013, we collected 1,118 Murray Cod and 1,742 Golden Perch by electrofishing and gillnetting. Values of k and L∞ were greater for reservoir fish than for riverine fish. For both species, AM50 was generally greater in rivers than in reservoirs; for Murray Cod, LM50 was greater in reservoirs than in rivers. A yield‐per‐recruit model demonstrated that smaller Murray Cod MLLs would be required for rivers and that an MLL at or below 600 mm (the existing MLL) across all populations could lead to overfishing in some systems. The differences in growth rate and the onset of reproductive maturation between riverine and reservoir populations suggest that system‐specific regulations would be more effective at reducing the overfishing risk and meeting fishing quality objectives. Received August 18, 2014; accepted September 10, 2015

A compendium of ecological knowledge for restoration of freshwater fishes in Australia

“…Declines in catches eventually saw all commercial fisheries closed by the early 2000s (Rowland 2005). Widely produced in hatcheries and stocked for recreational fishing (Rowland 2005;Ingram et al 2011;Forbes et al 2015aForbes et al , 2015bHunt and Jones 2018), Murray cod have been translocated and stocked outside the MDB (Cadwallader and Gooley 1984), as well as farmed for human consumption (Haldane 2014). There has been a partial recovery of populations in some areas, and the species was not considered threatened in the 2019 IUCN Red List assessment , but there have been numerous large-scale fish kills in the past two decades (Koehn 2005b;King et al 2012;Thiem et al 2017;Vertessy et al 2019).…”

Managing threats to freshwater systems within protected areas

“…Subsistence fisheries may be regulated by community co-management frameworks (Panayotou 1982). Recreational fisheries are controlled via harvest restrictions such as size or bag limits as well as seasonal closures to protect sensitive life history events such as spawning aggregations, parental care, etc (Forbes, Watts et al 2015). Illegal fishing is generally combated using strong compliance frameworks, although there is evidence that non-mandated regulations can also be effectively applied (Cooke, Suski et al 2013).…”

Volitional Spawning of Captive‐Reared Age‐4 Alligator Gars

“…Fisheries managers will also benefit from additional information on the life history and reproductive biology of an actively managed species such as Alligator Gar. Information supporting accurate and current estimates of age and size at maturity is valuable in refining the tools used to make management decisions (Ferguson et al 2014;Forbes et al 2015). To our knowledge, the successful reproduction within the captive population of knownage Alligator Gars described in this paper represents the earliest confirmed age at sexual maturity for the species.…”

“…; Forbes et al. ). To our knowledge, the successful reproduction within the captive population of known‐age Alligator Gars described in this paper represents the earliest confirmed age at sexual maturity for the species.…”