Sciaenid Aggregations in Northern Australia: an Example of Successful Outcomes through Collaborative Research

Aggregations of the Sciaenid, Black Jewfish (Protonibea diacanthus), off Muttee Head in far northern Cape York Peninsula (CYP), have been exploited by Indigenous subsistence fishers for over fifty years. The apparent recent increase in effort targeting P. diacanthus in CYP’s Northern Peninsula Area (NPA), has prompted concerns for the Injinoo Aboriginal Community, which has custodial responsibilities for that stock, and for the Queensland Fisheries Service, who must provide for managing fisheries in Queensland on a sustainable basis. The tendency of P. diacanthus to aggregate annually in large numbers at well defined times and locations appears to facilitate the harvest of the species. In 1999, 96% of the recorded catch of this fish in the NPA (3.91 tonnes) occurred between April and August, the period in which historical accounts suggest they aggregate in the area. In 2000, 89% of the recorded catch (4.46 tonnes) occurred between May and September. Catches in 1999 and 2000 commonly exceeded 50 P. diacanthus per boat, with CPUE peaking at 224.5 kg boat h-1. The relative ease of catching Black Jewfish when aggregating may render them susceptible to over-exploitation. Based on length-age keys of Bibby and McPherson (1998), the predominant size and age represented in catches from Muttee Head during the aggregation period fell from three year old stock in 1999 to two year old stock in 2000. Historical records reveal that specimens close to the maximum size (>1500 mm TL) were being caught up until 1994. These data support the notion of a rapid change in the NPA Sciaenid resource, and justify concern for the state of the resource given that the fishery was previously based on adult stock. Sexually mature P. diacanthus comprised only a small component (12 fish out of 270 = 4.4%) of the NPA catch examined in a sampling program that was biased towards the largest individuals available. The present study observed a minimum size at first maturity of 790 mm TL for female P. diacanthus. This represents a significant departure from the previous observed first length at maturity in Queensland waters of 920 mm TL, reported by McPherson (1997). A mark and release program, analysis of the diet, and examination of the genetic population structure contributed to the findings. In response to the research findings of the present project, the Injinoo Land Trust (representing the Traditional Land Owner Groups of the Anggamuthi, Atambaya, Gudang and Yadhaykenu Aboriginal people), in cooperation with the Injinoo Community Council, have selfimposed a two-year ban on the taking of Black Jewfish. The area of closure incorporates the inshore waters of the NPA north of the southern boundaries of Crab Island (on the West Coast) and Albany Island (on the East Coast). The aim of the two-year ban is to allow local Black Jewfish stocks to reach a mature size so that prospects for the replenishment of stocks are improved. With much consultation, this imitative has developed into a regional agreement with comprehensive support across the NPA. Representing each of the communities of the NPA, the Community Councils of Umagico, Bamaga, New Mapoon and Seisia, have undertaken to participate in the two-year ban on the take of P. diacanthus. In order to gain legislative backing for this species-specific ban, each of the Indigenous communities have expressed a willingness to forfeit their statutory exemption from the relevant catch restrictions. The implementation of the two-year closure presents new opportunities and obligations for research and management agencies alike to meet highly developed public expectations.