Tales of fish from ear bones and historical archives
The term shifting baseline was first used by the fisheries researcher Daniel Pauly in 1995 (Pauly 1995) to describe the way in which changes to an ecological system are measured against past baselines which in themselves may already represent significant change within a system. When measuring the extent of degradation in systems, researchers tend to use the state of that system at the beginning of their careers, or a few decades previously, as the baseline rather than the system in its original state, that is, prior to any interference by humankind. In this way, long term and significant decline in an ecosystem (or fishery) will be unintentionally disguised (Dayton et al. 1998; Pitcher 2001).
Since Pauly (1995) alerted researchers to the shifting baseline syndrome, scientists have been attempting to conduct research into terrestrial and marine ecology using new baselines that reflect more realistically the organisms and their habitats prior to human disturbance. Unless these more appropriate baselines are investigated, established and used, there is a danger that future generations will regard an ocean dominated by jellyfish and bacteria the norm (e.g. Lynam et al. 2006, Richardson et al. 2009). To combat this syndrome, we need information from earlier time periods, which may be available via historical data. In fish, an excellent source of such data are ear bones (otoliths) and scales, which are found in sedimentary deposits and Aboriginal middens, and can store environmental information in the form of chemical signatures.
Australia has been colonised and industrialised for long enough for significant baseline shifts to have occurred, producing skewed understanding of fish habitats, numbers and behaviours. Researchers in the Gillanders Aquatic Ecology laboratory have been using otoliths from archaeological midden sites to estimate fish size (and age) and provide information on growth and environmental conditions encountered by fish from thousands of years ago (e.g. Disspain et al. 2011, 2012, 2017, 2018; Izzo et al. 2017). More recently, we have also recognized the importance of historical newspaper archives to help bridge the gap between archaeological samples and modern day collections (e.g. Alleway et al. 2016; Disspain et al. 2018).
Our recent paper (Disspain et al. 2018) investigates how mulloway populations in waters of eastern South Australia have changed in terms of size, age and growth using information from archaeological fish otoliths (1670–1308 cal BP to 409–1 cal BP), historical anecdotes (CE 1871–1999), and contemporary data sources (CE 1984–2014). Our results found no significant changes in fish length (see figure above) through time with the maximum recorded sizes being similar across all three time periods, but that the abundance of these large specimens may have declined. This study demonstrates the benefits of combining multiple data sources to examine fish dynamics over thousands of years.
Dayton et al. 1998. Sliding baselines, ghosts and reduced expectations in kelp forest communities. Ecological Applications 8: 309-322.
Disspain et al. 2018. Long-term archaeological and historical archives for mulloway, Argyrosomus japonicus, populations in eastern South Australia. Fisheries Research 105, Sept 2018, pages 1-10.
Disspain et al. 2017. Pre-Columbian fishing on the coast of the Atacama Desert, northern Chile: An investigation of fish size and species distribution using otoliths from Camarones Punta Norte and Caleta Vitor. Journal of Coastal and Island Archaeology 12: 428-450.
Disspain et al. 2012. Morphological and chemical analysis of archaeological fish otoliths from the Lower Murray, South Australia. Archaeology in Oceania 47: 141-150.
Disspain et al. 2011. Developing baseline data to understand environmental change: a geochemical study of archaeological otoliths from the Coorong, South Australia. Journal of Archaeological Science 38: 1842-1857.
Izzo et al. 2017. Seasonally resolved environmental reconstructions using fish otoliths. Canadian Journal of Fisheries and Aquatic Sciences 74: 23-31.
Lynam et al. 2006. Jellyfish overtake fish in a heavily fished ecosystem Current Biology 16: R492-493.
Pauly 1995. Anecdotes and the shifting baseline syndrome of fisheries. Trends in Ecology and Evolution 10: 430.
Pitcher 2001. Fisheries managed to rebuild ecosystems? Reconstructing the past to salvage the future. Ecological Applications 11: 601-617.
Richardson et al. 2009. The jellyfish joyride: causes, consequences and management responses to a more gelatinous future. Trends in Ecology and Evolution 24: 312-322.
Photo - Women with mulloway from Glenelg River around 1915