Using their heads - A novel, collaborative approach between industry and scientists to monitor a commercial mullet fishery as a result of COVID-19 restrictions.

The COVID-19 global pandemic-related restrictions during 2020 severely impacted the Australian seafood industry, including essential scientific monitoring to support stock assessment and to demonstrate sustainability. Here we detail a novel, collaborative monitoring program between scientists and the seafood industry to generate length and age compositions that were representative of one of the largest, most valuable, and controversial fisheries along eastern Australia, the pre-spawning ocean run fishery for Sea Mullet Mugil cephalus that is predominantly a roe fishery. The standard approach to monitoring this fishery has been to base trained scientific staff at the major processing facility for M. cephalus, where they access whole fish from entire catches to generate representative length and age compositions during the peak season, April to May. Covid-19 restrictions prevented this approach for 2020 in eastern Australia. In recognition that in addition to the high-value roe, all components of the female fish are utilized (heads and guts for bait, bodies for human consumption), a multi-stage, spatially stratified sampling design was investigated. Female heads were retained from randomly selected catches from each of the three major fishing zones and transported to the New South Wales Department of Primary Industries fish laboratory based in Sydney. Head lengths (HLs) were measured and converted to Fork Lengths (FLs) using a HL to FL relationship. The resulting fish length compositions from each catch were subsequently combined based on: (i) relative catch size of females within an ocean zone, and; (ii) the relative reported landings of females in each ocean fishing zone. Otoliths were randomly collected from heads sampled from each ocean zone and used to estimate age. The resulting ocean zone to age matrix was combined with the relative reported landings of female fish in each ocean fishing zone to generate a total female age composition for the fishery. The estimated age composition of females were typical in being mainly between ages 3 and 6, with a strong presence of 4-year olds. This stronger cohort was present as 3-year olds in 2018/19 and 5-year olds in 2020/21, thus providing confidence that our sampling was representative of the fishery. The study reinforces the positive outcomes that can be generated through co-management between scientists and the seafood industry.

Geographical variation in age and growth of the endemic Australian sciaenid Atractoscion atelodus.

Growth rates and other age-related population characteristics are essential parameters underpinning management of a stock. This is the first study to estimate length-at-age of Atractoscion atelodus (family Sciaenidae) in New South Wales (NSW), despite the species being exploited since the 1940s. The aim of the current study was to quantify the age-based biological characteristics of A. atelodus and in particular: (a) validate the use of sagittal otoliths to quantify age; (b) estimate the growth rates and longevity of males and females; (c) examine geographical variation in age and growth; (d) document the age composition in commercial landings and (e) estimate mortality rates. A. atelodus is relatively fast growing, reaching 40 cm fork length (LF ) in the first year of life and living to at least 14 years. Growth was significantly different between sexes, with modelled asymptotic lengths of females (L∞  = 84.6 cm LF ) greater than males (L∞  = 69.0 cm LF ). Growth rates were also significantly different between northern and southern populations. Fish sampled from the southern region were younger and faster growing than those sampled in the northern region, supporting the counter-gradient growth theory and the influence of upwelling providing greater nutrient and food availability. The commercial fishery was predominantly based on young fish <3 years. with few (c. 5%) greater than 5 years. Fishing mortality estimates (F = 0.42) were similar to natural mortality estimates (M = 0.44). The age-based parameters estimated in the present study suggest that A. atelodus should be relatively resilient to fishing; nonetheless, the sizes and ages in landings are indicative of a stock heavily fished. The fishery is experiencing truncated age distributions and appears to be largely recruitment driven, increasing susceptibility to overexploitation. Determining geographical differences in growth rates of a population has important implications when considering impacts of anthropogenic drivers such as global warming and overexploitation and is important to determine in managing exploited fish populations.

The influence of climatic and lunar drivers on landings cycles of the temperate Australian sciaenid (Atractoscion atelodus) at two temporal scales: A working hypothesis for future management of this resource.

Commercial line-fishing catch rates of the endemic sciaenid Atractoscion atelodus in eastern-Australia were significantly affected by lunar phase. Periodic regression analysis indicated that catch rates were greatest during the full moon period and lowest during the new moon period. It is hypothesized that this observation is the result of the visual nocturnal feeding nature of A. atelodus, with schools of fish using the increased ambient light in the water column during the brighter part of the lunar phase to feed intensively. Increased feeding intensity during the brighter phase of the lunar month may also be related to spawning activity during the new moon phase; however this hypothesis remains to be tested. Annual commercial landings through a 71 year dataset (1950-2020) showed an approximately exponential decline, overlaid with periodic years of higher and lower landings. Such periods of higher landings were significantly positively correlated with coastal rainfall two and three years earlier, but not with rainfall in the same year or one, four or five years earlier. We hypothesize that increased coastal rainfall, likely in combination with unknown co-occurring factors, promotes increased recruitment success of A. atelodus, potentially through increased primary productivity in the nearshore marine environment. This translates into an increase in the fishable stock mainly two and three years later. If our hypothesis is correct, climate predictions of reduced rainfall in eastern Australia suggest a pessimistic outlook for this fishery.