Estimating the value of tropical coastal wetland habitats to fisheries: Caveats and assumptions

Abstract

Habitat valuation can provide an objective basis for the prioritisation of conservation and restoration actions. The attribution of fisheries production to particular habitat units is an important measure of value, but is difficult to estimate. Using the case study of habitat use by juvenile banana prawns in a tropical estuary, we assessed the potential to produce valid value estimates at two spatio-conceptual scales: estuary reach and whole estuary. Additionally, we also explore the potential to produce meaningful value estimates at the scale of whole estuary contribution to the offshore fisheries stock. A diversity of potential and actual sources of error and logical problems means that quantification at any scale is at best of uncertain validity and produces estimates that are likely to produce unreliable results if treated as quantitative inputs to production models. Estimates for the whole estuary were the most viable, although still requiring substantial assumptions that may or may not be reasonable in particular situations. Estimates for individual habitats required the unreasonable assumption of limited prawn movement, while estimates of contribution of an estuary to the fishery required difficult-to-obtain and usually unavailable information. Because low occupancy habitats can have trophic value, we also used stable isotope analysis to assess the importance of mangroves and saltmarshes to prawn nutrition. No particular habitat was of critical trophic importance, again suggesting that the habitat-production link is most usefully assessed at the whole-of-estuary scale. While valuable and required to support targeted ecosystem management and protection and restoration efforts, valid estimates of the contribution of particular units to fisheries are likely to be unachievable in many situations.

Priorities and Motivations of Marine Coastal Restoration Research

“…Ecological restoration or "the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed" (SER, 2004) is urgently needed to assist ecosystems where natural recovery is hindered or impeded (Perrow and Davy, 2002). Ecological restoration principally seeks to recover the functioning of degraded ecosystems, however restoration of marine and coastal habitats can provide a range of ecological and socio-economic benefits, such as coastal protection from flooding and erosion, fisheries habitat, water quality improvements, and carbon sequestration and storage (Duarte et al, 2013;Fodrie et al, 2017;Macreadie et al, 2017;Abrantes et al, 2019;Gilby et al, 2020). The United Nations General Assembly recently declared the "UN Decade on Ecological Restoration" for 2021-2030 and ecological restoration is on the rise as a component of the solution to ameliorate ecosystem degradation (Possingham et al, 2015).…”

Prospects for seascape repair: Three case studies from eastern Australia

“…In comparison, estimates at the whole‐of‐estuary level, the seascapes level, in line with current understanding of estuarine species reliance on a mosaic of habitats (Nagelkerken et al ; Sheaves ), required a relatively low number of assumptions and produced estimates with relatively low variability. Abrantes et al () found as a conservative estimate, a maximum juvenile prawn biomass of 6.5 g/m 2 for the 2 m wide bands along the estuary edge where prawns are found. For the estuary studied, with an edge area of 5.6 ha, the conservative total biomass of juvenile pawns was 0.36 tonnes.…”

“…The east coast tropical study (Abrantes et al . ) found that estimates of productivity of individual components of the estuary were highly variable and depended on a number of assumptions, which are difficult to validate (Rönnbäck et al ; Minello et al ; Rozas & Minello ). In comparison, estimates at the whole‐of‐estuary level, the seascapes level, in line with current understanding of estuarine species reliance on a mosaic of habitats (Nagelkerken et al ; Sheaves ), required a relatively low number of assumptions and produced estimates with relatively low variability.…”

“…To address our questions, we used three case studies (Taylor & Creighton ; Prahalad et al ; Abrantes et al . ) developed as part of a research program supported by Australian Government’s National Environmental Science Program. The case studies span a range of biophysical and policy settings across tropical, subtropical and temperate Australia (Figs , , Table ).…”

Short Communication: The presence of Bull shark Carcharhinus leucas (Elasmobranchii: Carcharhinidae) in the fresh waters of Sumatra, Indonesia

“…Osmoregulation in C. leucas is achieved through the control and integration of various organs such as the liver and kidney in response to salinity changes. However, little is known regarding the mechanisms of ion transport in the gills of euryhaline C. leucas and how they are affected by osmoregulatory challenges (Hazon et al 2003;Evans et al 2004) Estuaries are biologically diverse and productive ecosystems that provide essential habitats for many fauna and flora including avertebrata, finfish, reptile, and amphibian (Paighambari et al 2017;Abrantes et al 2019). Characterized by shallow water and intertidal areas, including mangrove forests, swamps, saltmarsh, seagrass, intertidal mudflats, and shallow sub-tidal habitats, they are transitional habitats between land and water and freshwater and marine environments (Thomas 2017;Dubuc et al 2019).…”