Marine resources are among the most important resources for humanity, whose demand will continue to increase as population increases. Consequently, effective and sustainable management is essential, as is learning from the past. Many fish species have been or are overexploited, and depending on their characteristics, they can recover partially, completely, or even not recover from this overexploitation.

In the Southern Ocean, fishing is now regulated and with effective management measures. However, this was not always the case, and in the 1960s and 1970s, on islands such as South Georgia or Kerguelen there were intensive fisheries, including the fishery of marbled rockcod (Notothenia rossi). This fish species inhabits between 0 and 400m deep and reaches an average length of 50 – 70cm. For example, over the years of 1969 and 1971, around 500 000 tons of captured fish were reported at South Georgia. Although this catch was likely included other species other than rockcod, it still represents a large catch. Additionally, part of the fishing was also illegal and incorrectly reported. All these factors dictated the depletion of this stock, which has dropped drastically, almost leading to the disappearance of marbled rockcod populations. Due to this, the fishery was no longer profitable as it was also banned, both in South Georgia and later in the Southern Ocean, an end dictated by the Commission for the Conservation of Living Marine Resources of Antarctica (CCAMLR).

A study by British researchers based on data from 23 years of sampling through research vessels, explored how the population of this species has or not recovered 50 years after its overexploitation. This analysis was performed based on numerous variables, from abundance, distribution, size, weight and age of individuals, sexual maturity, as well as their diet.

Recovered population?

The researchers found that marbled rockcod population has managed to recover and restore healthy levels. However, such recovery only began after 2005, 35 years after the overexploitation. It has taken 3 to 4 generations (6-8 years per generation) for the population to stabilize and be able to gradually grow. Several factors are associated with this recovery as well as with its possible delay. Among these are the fishery ban, the plasticity of their diet and the occupation of new areas with more prey. The delay of several decades for this recovery is attributed in part to the late sexual maturity in this species, the recovery of a considerable predator during this period, the Antarctic fur seal (Arctocephalus gazella), and the possibility that the South Georgia ecosystem may not have the same carrying capacity to sustain as much biomass as in the 60s and 70s, due to the environmental changes that have been impacting the region.

Therefore, despite past errors in the Antarctic Ocean, in this case South Georgia, this study shows that after implementing science-based management and strict measures it is possible, in the long term, for a species to recover and establish itself again in the ecosystem. A model that can serve as an example for other places.

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Source: Hollyman, Philip R., et al. “A long road to recovery: dynamics and ecology of the marbled rockcod (Notothenia rossii, family: Nototheniidae) at South Georgia, 50 years after overexploitation.” ICES Journal of Marine Science 78.8 (2021): 2745-2756. DOI: 10.1093/icesjms/fsab150

Author: José Abreu