Management adaptation of invertebrate fisheries to an extreme marine heat wave event at a global warming hot spot

Abstract

An extreme marine heat wave which affected 2000 km of the midwest coast of Australia occurred in the 2010/11 austral summer, with sea-surface temperature (SST) anomalies of 2-5°C above normal climatology. The heat wave was influenced by a strong Leeuwin Current during an extreme La Niña event at a global warming hot spot in the Indian Ocean. This event had a significant effect on the marine ecosystem with changes to seagrass/algae and coral habitats, as well as fish kills and southern extension of the range of some tropical species. The effect has been exacerbated by above-average SST in the following two summers, 2011/12 and 2012/13. This study examined the major impact the event had on invertebrate fisheries and the management adaption applied. A 99% mortality of Roei abalone (Haliotis roei) and major reductions in recruitment of scallops (Amusium balloti), king (Penaeus latisulcatus) and tiger (P. esculentus) prawns, and blue swimmer crabs were detected with management adapting with effort reductions or spatial/temporal closures to protect the spawning stock and restocking being evaluated. This study illustrates that fisheries management under extreme temperature events requires an early identification of temperature hot spots, early detection of abundance changes (preferably using pre-recruit surveys), and flexible harvest strategies which allow a quick response to minimize the effect of heavy fishing on poor recruitment to enable protection of the spawning stock. This has required researchers, managers, and industry to adapt to fish stocks affected by an extreme environmental event that may become more frequent due to climate change.

Keywords: Climate change; crabs; environmental effects; prawns; pre‐recruit; scallops; stock‐recruitment; water temperature.

Figure 1

Map of Western Australia showing key locations and location of fisheries.

Figure 2

(A) Summer (December–February) sea‐surface temperature (SST) for 1^o blocks off Western Australia on the west coast near Ningaloo, Shark Bay, Abrolhos Is., Rottnest Is., and the Capes region, and the south coast near Albany and Esperance. (B) Summer SST anomalies for the above locations.

Figure 3

Monthly sea‐surface temperature (SST) anomalies relative to 1982–2012 mean temperatures based on the 28 km resolution OIv2 dataset for February (A–D) and June (E–H) and temperature contours are shown at 0.5°C intervals. The names in (A) represent SST locations in Exmouth Gulf (ExNw), Shark Bay (DS50), and Abrolhos Is. (Ceaster).

Figure 4

Shark Bay Blue swimmer crabs: Relationship between the annual standardized commercial trap catch rate (year t/t + 1) and mean summer sea‐surface temperature (SST) during juvenile phase and peak spawning period in the previous winter. The year of the catch rate is shown with the winter (April–August) SST. The solid triangle represents predicted catch rates for 2012/13 and 2014/15.

Figure 5

Shark Bay scallops: Relationship between pre‐recruit (0+) November survey catch rate and sea‐surface temperature (SST) in the previous summer (December–January) (top). The recruit year is shown. Relationship between the pre‐recruit index (log‐transformed) with the spawning stock index (bottom). The recruit year is shown with the points indicating whether the SST during December–January is above or below 24°C. The predicted pre‐recruit abundance for 2015 based on the spawning stock and SST is also indicated.

Figure 6

Positive and negative relationship between king prawn recruitment (year t) and sea‐surface temperature (SST) (November year t−1 to April year t) in Shark Bay (top) and SST (November–December in year t−1) in Exmouth Gulf, respectively (bottom). The recruitment year is indicated.