Estimating fishing and natural mortality rates, and catchability coefficient, from a series of observations on mean length and fishing effort

Gedamke and Hoenig (2006) (Transactions of the American Fisheries Society, 135: 476-487) developed a non-equilibrium version of the Beverton and Holt estimator of total mortality rate, Z, based on mean length and thereby increased the usefulness of length-based methods. In this study, we extend their model by replacing period-specific Z parameters with the year-specific parameterization Z(y) = qf(y) + M where q is the catchability coefficient, f(y) is the fishing effort in year y, F (= qf) is the fishing mortality rate, and M is the natural mortality rate. Thus, the problem reduces to estimating just three parameters: q, M and residual variance. We used Monte Carlo simulation to study the model behaviour. Estimates of q and M are highly negatively correlated and may or may not be reliable; however, the estimates of corresponding Z\u27s are more precise than estimates of F and are generally reliable, even when uncertainty about the mean lengths is high. This length-based method appears to work best for stocks with rapid growth rate. Contrast in effort data may not be necessary for reliable estimates of Z\u27s. This approach forms a bridge between data-limited models and more complex models. We apply the method to the Norway lobster Nephrops norvegicus stock in Portugal as an example

Evaluating the predictive performance of empirical estimators of natural mortality rate using information on over 200 fish species

Many methods have been developed in the last 70 years to predict the natural mortality rate, M, of a stock based on empirical evidence from comparative life history studies. These indirect or empirical methods are used in most stock assessments to (i) obtain estimates of M in the absence of direct information, (ii) check on the reasonableness of a direct estimate of M, (iii) examine the range of plausible M estimates for the stock under consideration, and (iv) define prior distributions for Bayesian analyses. The two most cited empirical methods have appeared in the literature over 2500 times to date. Despite the importance of these methods, there is no consensus in the literature on how well these methods work in terms of prediction error or how their performance may be ranked. We evaluate estimators based on various combinations of maximum age (t(max)), growth parameters, and water temperature by seeing how well they reproduce \u3e200 independent, direct estimates of M. We use tenfold cross-validation to estimate the prediction error of the estimators and to rank their performance. With updated and carefully reviewed data, we conclude that a t(max)-based estimator performs the best among all estimators evaluated. The t(max)-based estimators in turn perform better than the Alverson-Carney method based on t(max) and the von Bertalanffy K coefficient, Pauly\u27s method based on growth parameters and water temperature and methods based just on K. It is possible to combine two independent methods by computing a weighted mean but the improvement over the t(max)-based methods is slight. Based on cross-validation prediction error, model residual patterns, model parsimony, and biological considerations, we recommend the use of a t(max)-based estimator (M = 4.899t(max)(-0.916), prediction error = 0.32) when possible and a growth-based method (M = 4.118K(0.73)L(infinity)(-0.33), prediction error = 0.6) otherwise

Properties of age compositions and mortality estimates derived from cohort slicing of length data

Cohort slicing can be used to obtain catch-at-age data from length frequency distributions when directly measured age data are unavailable. The procedure systematically underestimates the relative abundance of the youngest age groups and overestimates abundance at older ages. Cohort-sliced catch-at-age data can be used to estimate total mortality rate (Z) using a regression estimator or the Chapman-Robson estimator for right truncated data. However, the effect of cohort slicing on accuracy and precision of resulting Z estimates remains to be determined. We used Monte Carlo simulation to estimate the per cent bias and per cent root mean square error of the unweighted regression, weighted regression, and Chapman-Robson mortality estimators applied to cohort-sliced data. Incompletely recruited age groups were truncated from the cohort-sliced catch-at-age data using previously established recommendations and a variety of plus groups was used to combine older age groups. The sensitivity of the results to a range of plausible biological combinations of Z, growth parameters, recruitment variability, and length-at-age error was tested. Our simulation shows that cohort slicing can work well in some cases and poorly in others. Overall, plus group selection was more important in high K scenarios than it was in low K scenarios. Surprisingly, defining the plus group to start at a high age worked well in some cases, although length and age are poorly correlated for old ages. No one estimator was uniformly superior; we therefore provide recommendations concerning the appropriate estimator and plus group to use, depending on the parameters characterizing the stock. We further recommend that simulations be performed to determine exactly which plus group would be most appropriate given the scenario at hand

Ecosystem service provision by marine habitats in Southeast Asia

Southeast Asia is an area of rich marine biodiversity providing a host of ecosystem services that contribute to the well-being of coastal communities and beyond. Sustainable management of ecosystems and the services they provide requires a good understanding of their underlying ecological functions and processes. This understanding can be gained through the rigorous assessment of studies identifying and quantifying ecological functions and ecosystem services. The aims of this study were to review the ecosystem services provided by marine and coastal habitats in Southeast Asia. The ecosystem service potential was scored for each habitat. The review was focused on nine key marine and coastal habitats, identified across four case study sites in Southeast Asia, contributing 18 marine relevant ecosystem services. The approach comprised a literature review supplemented with observations from experts from the case study areas. The four case study sites consist of three Man and Biosphere Reserves in Southeast Asia: Palawan in the Philippines, Cu Lao Cham- Hoi An in Viet Nam, Take-Bonerate Kepulauan Selayar in Indonesia, and a recently gazetted marine protected area, the Tun Mustapha Marine Park in Malaysia (Figure 1). The nine key habitats (eight benthic and one pelagic) covered in this review, identified as highly relevant for most case study sites, were mangrove forests, coral reefs, seagrass meadows, sand, mud, rock, coarse substratum, pelagic and modified habitats. Further division of these habitats into sub-habitats on the basis of biological type and substrate type was used to capture data on differential provision of ecosystem services within the broad habitat types. To ensure relevance in the four case study sites, firstly an ecosystem services typology was created tailored to these sites. After exploring several ecosystem service typologies, our final classification was adapted from the Common International Classification of Ecosystem services (CICES) V4.3 because it was considered to be most relevant to the objectives of this task. Provisioning, regulation and maintenance, and cultural services were assessed. Provisioning services focused on food for consumption by humans from plants, pelagic animals, demersal fish and invertebrates; energy from harvested plants; other materials from plants and animals, such as fibres, building and housing materials, medicines, decoration, handicrafts and souvenirs; and genetic material from plants and animals (including seeds, spat, spores, whole plants or animals, individual genes), for example seed or brood-stock collection for aquaculture and mangrove replanting and new plantations. Regulation and maintenance services assessed were treatment and assimilation of wastes or toxic substances; coastal erosion control; water flow regulation contributing to dampening the intensity of storm, floods, tsunamis, and hurricanes and the maintenance of localized water flows such as coastal current structures; maintenance of nursery,reproduction and feeding habitats; maintenance of critical habitats for charismatic species such as turtles, dugongs, cetaceans, sharks, seahorses, bats, fireflies, birds, monkeys, orchids and other epiphytes; and climate regulation through impacts on the hydrological cycle, temperature regulation, and the contribution to regulation of climate-influencing gases in the atmosphere, for example through carbon sequestration and long-term, decadal storage. Cultural services examined included uses of habitats as places for active and passive recreation; ceremonial activities; creative activities; and knowledge-based activities, such as educational activities, and citizen science or community environmental activities. The comprehensive literature review included peer-reviewed scientific research literature as well as grey literature such as government and other reports. To ensure a wide breadth of coverage, the research focused on studies from Southeast Asia. When no evidence was found in the literature, evidence was sought from experts, and where useful, was accompanied by observations from the authors in their respective case study sites. The evidence gathered was used to assess the potential of each habitat to provide an ecosystem service, rather than to assess the actual provision of ecosystem services from each case study site. This important distinction allows the differentiation between services provided by the ecosystem (i.e. the potential supply of ecosystem services that a habitat could deliver) and (achieved or used) benefits (i.e. the demand for ecosystem services). The knowledge gained from the literature, local and regional reports, together with observations from the study team and experts, was critically assessed using a robust methodology that captured different types of information together with a confidence score for the supporting evidence. The contribution of each habitat to each ecosystem service was then scored relative to other habitats. Our objective was to provide baseline information to enable better understanding of the ecosystem services arising from marine and coastal habitats in SE Asia. This provides a foundation for future assessments of natural capital and ecosystem services which may be used to inform sustainable management. The report will serve as a useful reference to many different readers. Regulators, managers of marine sites and policy makers might use this report to inform their management choices. This should enable more sustainable use of the marine environment and maximise the ecosystem service provision of all types of services addressed in this study. Stakeholders of the marine environment such as fisherfolk or residents might use this report to help them engage in management processes, to gain deeper understanding of the marine environment or confirm their observations of the marine environment. Academics can use it as a reference source or a base for further studies, in particular for valuation studies or when considering the trade-offs between ecosystem services in marine and coastal habitats. Finally, it is hoped that this report may bring a new appreciation and understanding of the marine environment and the life support it provides to society and inspire readers to improve management of the marine environment. This report is one of the outputs of the UK Research and Innovation’s Global Challenges Research Fund (UKRI GCRF) Blue Communities Programme (GCRF Blue Communities Global Challenges Research Fund via the United Kingdom Research and Innovation (UKRI) under grant agreement reference NE/P021107/1, www.blue-communities.org), which aims to “build capacity for sustainable interactions with marine ecosystems for the benefit of the health, well-being, food security and livelihoods of coastal communities in SE Asia”. GCRF Blue Communities is developing interdisciplinary research capability and lasting collaborations that can facilitate innovative application of integrated planning in the marine environment and respond to the UN Sustainable Development Goals of ‘no poverty’, ‘zero hunger’, ‘good health and well-being’ for coastal communities as well as ‘conserve and sustainably use the oceans, seas and marine resources for sustainable development’ through the sustainable use of marine resources

Building bridges between natural and social science disciplines: a standardized methodology to combine data on ecosystem quality trends

Despite a growing interest in interdisciplinary research, systematic ways of how to integrate data from different disciplines are still scarce. We argue that successful resource management relies on two key data sources: natural science data, which represents ecosystem structure and processes, and social science data, which describes people’s perceptions and understanding. Both are vital, mutually complementing information sources that can underpin the development of feasible and effective policies and management interventions. To harvest the added value of combined knowledge, a uniform scaling system is needed. In this paper, we propose a standardized methodology to connect and explore different types of quantitative data from the natural and social sciences reflecting temporal trends in ecosystem quality. We demonstrate this methodology with different types of data such as fisheries stocks and mangrove cover on the one hand and community’s perceptions on the other. The example data are collected from three United Nations Educational Scientific and Cultural Organization (UNESCO) Biosphere reserves and one marine park in Southeast Asia. To easily identify patterns of convergence or divergence among the datasets, we propose heat maps using colour codes and icons for language- and education-independent understandability. Finally, we discuss the limitations as well as potential implications for resource management and the accompanying communication strategies. This article is part of the theme issue ‘Nurturing resilient marine ecosystems’

MALAYSIA AND SELANGOR MANGROVE POLICY MAPPING AND ANALYSIS

Executive Summary Purpose of the report • This report presents an overview of a policy mapping activity which considers local, state, federal and international plans, laws, policies, and directives that influence the conservation and management of mangroves in Malaysia. • The key actors that play an important role in mangrove policy creation and delivery are also mapped. • To reflect Malaysia’s federal system of government, the state of Selangor in Peninsula Malaysia is used as a case study to show how mangrove policies and actors span these decision-making levels. • The report identifies policy gaps and makes recommendations on how the policy landscape can be modified to support the sustainable management of mangroves within state and federal levels in Malaysia. Method • Relevant policy instruments and policy actors are identified through application of a Rapid Policy Network Mapping (RPNM) approach. • This approach enables visualisation of the mangrove policy landscape through the creation of policy instrument and policy actor maps. • The policy instrument map plots instruments by policy domain (international, regional, national, or local (state) scales), and policy category (cross-sectoral, forestry, fisheries, tourism, other environmental and non-environmental). • The policy actor map plots actors by policy domain and policy role (Influencer, Owner/Decision-Maker, Influencer/Deliverer, Deliverer. • A database of instruments and actors was also generated to record characteristics of both elements, which can become a resource for future policy assessments. Results • Forty-one policy instruments and forty-six policy actors are identified from this approach as influencing mangrove management to the state level. • The highest policy instrument activity occurs at the national level and within a crosssectoral context (i.e., biodiversity). Only five instruments are identified at the state level. • No fisheries/aquaculture instruments are featured through this process. • The highest number of policy actors operate at national level and are equally distributed across the roles of Influencer, Owner/Decision-maker, and Influencer/Deliverer. Policy gaps and key recommendations • To recognise the importance of mangroves in providing multiple benefits to a range of parties across sectors, and to the environment, existing influential policies (i.e. National Forestry Policy, National Biodiversity Policy), as well as those in the process of review (i.e. National Climate Policy, National Wetland Policy), should be strengthened with regard to the explicit priority afforded mangroves, enabling: o Appropriate resource allocations. o Potential economies of scale through harmonisation of policy priorities that deliver co-benefits. o Greater understanding of the role mangroves can play in nature-based solutions for major global and national environmental threats, including climate change pressures, biodiversity loss, greenhouse gas (GHG) emission reductions and achievement of nationally determined contributions (NDC) targets. • A National Mangrove Policy would offer a significant statement in federal recognition of the importance of this specific forest (wetland) habitat. Alternatively, the creation of a National Blue Carbon Policy could present a more coordinated and broader-looking directive for developing programmes and projects that address the environmental challenges listed above. • A more explicit connection is needed between forestry and fishery policies to reduce the chances of mangrove (and mangrove-dependent resource) management falling through cracks of responsibility. • State authorities could publish policy implementation plan updates more frequently to show more transparency on progress against targets. • Further mapping exercises should be developed that comprehensively capture emerging federal and state circumstances to update these policy maps to improve their accuracy and relevance. • To capture variation in policy interpretation and implementation across these substate administration units, it is recommended that policy instruments of decisions made at this level are also mapped and analysed in order to improve consistency of application across the state