Multi-species Indicators Research Articles

Length-based indicators of fishery and ecosystem status: Glover's Reef Marine Reserve, Belize

For the spear gun fishery at Glover's Reef, Belize, we used catch length frequencies to infer whether each of the eight most common species was likely to be overfished (spawning stock biomass<target) or experiencing overfishing (fishing mortality rate F>natural mortality rate M). We used Monte Carlo simulations to determine whether the results were sensitive to uncertainty about natural mortality, asymptotic length, growth rate and length at maturity. We found that black grouper Mycteroperca bonaci is overfished, and Nassau grouper Epinephelus striatus, schoolmaster snapper Lutjanus apodus and mutton snapper Lutjanus analis are probably overfished, but hogfish Lachnolaimus maximus, stoplight parrotfish Sparisoma viride, French angelfish Pomacanthus paru and gray angelfish Pomacanthus arcuatus are probably not overfished. All species except French angelfish were experiencing overfishing across a range of life history parameters. Nassau grouper, black grouper and mutton snapper were often caught below the size at maturity Lm. The results were sensitive to different assumed values of the life history parameters. Life history parameters can vary regionally for many reef fishes, and there have been few life history studies in the western Caribbean; such studies would greatly improve estimates of stock status. We also calculated six multispecies indicators of fishery status. The mean length relative to Lm was greater than 1.0 and constant between 2005 and 2011. Mean trophic level, mean maximum size, and fraction piscivores increased between 2005 and 2011, partly due to the fact that parrotfish, previously an important component of the catch, have been prohibited beginning in 2009. Mean catch per unit effort declined. Given that black grouper, Nassau grouper, mutton snapper and schoolmaster snapper are found to be overfished and experiencing overfishing under most values of the life history parameters, we recommend size or catch limits for these species.

Priceless prices and marine food webs: Long-term patterns of change and fishing impacts in the South Brazil Bight as reflected by the seafood market

The lack of market variables in fishery systems (i.e., prices and quantities) has often been cited as one reason for the particular difficulty of understanding whole marine ecosystem change and its management under a broader ecosystem perspective. This paper shows the results of efforts to tackle this problem in the South Brazil Bight by compiling and analyzing in-depth an unprecedented 40-year database from the region’s largest wholesale seafood market, based in the megacity of São Paulo. Fishery landings and market values for the period 1968–2007 were analyzed primarily by updated trophic level classes and multispecies indicators including the (1) marine trophic index (MTI), (2) weighted price, and (3) log relative price index (LRPI) which relates prices and trophic levels. Moreover, an inferential analysis of major seafood category statistical trends in market prices and quantities and their positive and negative correlations was undertaken. In general, these market trends contributed substantially to identifying and clarifying the changes that occurred. Considerations of the behavior of demand, supply and markets are included. In particular, while the MTI did not support a “fishing down the marine food web” hypothesis, other indicators did show the continued scarcity of major high trophic level categories and fisheries target species. Overall, the results indicate that the analysis of fishery landings, or of certain other indicators alone, can mask real changes. Rather, a joint ecological–econometric analysis provides better evidence of the direction of ecosystem pressures and stock health. This method for detecting market changes across the food web may be particularly helpful for systems considered data-poor but where fish market data have been archived. This study further elucidates historical changes and fishing impacts in the South Brazil Bight ecosystem.

Development of multi-species indicators for the Nevada Wildlife Action Plan

Wildlife managers, conservationists, and policy-makers are interested in indicators that aggregate population status and/or trend information for multiple species. Several multi-species indicators have been proposed, which either report species status ranks or rank changes (using either the International Union for the Conservation of Nature or NatureServe ranking systems), or which report the average direction or tendency of time series from multiple populations or species. We explore the utility of these indicators within the context of the Nevada Wildlife Action Plan, one of 56 state or territorial wildlife conservation plans that have recently been developed and published by state wildlife agencies in the USA. The Nevada Wildlife Action Plan identifies 186 “species of greatest conservation need,” including birds, mammals, reptiles, amphibians, fish, and mollusks. Significant deficiencies in the existing monitoring data for these taxa limit the applicability of nearly all of the multi-species indicators that have been described to date. However, we were able to populate a simple multi-species status indicator with data for all 186 species. We also describe a simple graphical indicator that summarizes information about the direction of population trends for suites of multiple species, and discuss how this tool could be populated with data in future revisions of the Nevada Wildlife Action Plan.

Butterfly monitoring in Europe: methods, applications and perspectives

Since the first Butterfly Monitoring Scheme in the UK started in the mid-1970s, butterfly monitoring in Europe has developed in more than ten European countries. These schemes are aimed to assess regional and national trends in butterfly abundance per species. We discuss strengths and weaknesses of methods used in these schemes and give examples of applications of the data. A new development is to establish supra-national trends per species and multispecies indicators. Such indicators enable to report against the target to halt biodiversity loss by 2010. Our preliminary European Grassland Butterfly Indicator shows a decline of 50% between 1990 and 2005. We expect to develop a Grassland Butterfly Indicator with an improved coverage across European countries. We see also good perspectives to develop a supra-national indicator for climate change as well as an indicator for woodland butterflies.

Developing indicators for European birds

The global pledge to deliver 'a significant reduction in the current rate of biodiversity loss by 2010' is echoed in a number of regional and national level targets. There is broad consensus, however, that in the absence of conservation action, biodiversity will continue to be lost at a rate unprecedented in the recent era. Remarkably, we lack a basic system to measure progress towards these targets and, in particular, we lack standard measures of biodiversity and procedures to construct and assess summary statistics. Here, we develop a simple classification of biodiversity indicators to assist their development and clarify purpose. We use European birds, as example taxa, to show how robust indicators can be constructed and how they can be interpreted. We have developed statistical methods to calculate supranational, multi-species indices using population data from national annual breeding bird surveys in Europe. Skilled volunteers using standardized field methods undertake data collection where methods and survey designs differ slightly across countries. Survey plots tend to be widely distributed at a national level, covering many bird species and habitats with reasonable representation. National species' indices are calculated using log-linear regression, which allows for plot turnover. Supranational species' indices are constructed by combining the national species' indices weighted by national population sizes of each species. Supranational, multi-species indicators are calculated by averaging the resulting indices. We show that common farmland birds in Europe have declined steeply over the last two decades, whereas woodland birds have not. Evidence elsewhere shows that the main driver of farmland bird declines is increased agricultural intensification. We argue that the farmland bird indicator is a useful surrogate for trends in other elements of biodiversity in this habitat.

Size-spectra as indicators of the effects of fishing on coral reef fish assemblages

The data requirements and resources needed to develop multispecies indicators of fishing impacts are often lacking and this is particularly true for coral reef fisheries. Size-spectra, relationships between abundance and body-size class, regardless of taxonomy, can be calculated from simple sizeabundance data. Both the slope and the mid-point height of the relationship can be compared at different fishing intensities. Here, we develop size-spectra for reef fish assemblages using body size- abundance data collected by underwater visual census in each of ten fishing grounds across a known gradient of fishing intensity in the Kadavu Island group, Fiji. Slopes of the size-spectra became steeper (F9,69=3.20, p<0.01) and the height declined (F9,69=15.78, p<0.001) with increasing fishing intensity. Regressions of numbers of individuals per size class across grounds were negative for all size classes, although the slope was almost zero for the smallest size class. Response to exploitation of each size class category was greatest for larger fish. Steepening of the slope with increasing fishing intensity largely resulted from reductions in the relative abundance of large fish and not from the ecological release of small fish following depletion of their predators. The slope and height of the size-spectrum appear to be good indicators of fishing effects on reef fish assemblages.

Review of indicators in fisheries management – a development perspective

A review of indicators for an ecosystem approach to fisheries management is presented, focusing on multispecies fisheries and limited resources for assessments and implementation, as often is the case in developing countries. Emphasizing the need to link indicators to management objectives, indicators from the literature are grouped into four categories, relating to the immediate fisheries resource base (single-species and multispecies indicators) and the wider ecosystem (habitat structure and ecosystem functioning). The usefulness of these indicators is assessed along three dimensions of acceptability among stakeholders, observability, and relation to fisheries management using a traffic light approach. The top ranking indicators are highlighted as a generally good start for any particular fishery management case. It is, however, argued that, even with similar management objectives, indicators need to be specific to both ecosystems and the institutional set-up if they are to be effective for management, and that indicators may consequently differ considerably between individual management applications.