Benefits of a restricted spatial and temporal survey design for determining average weight of recreational catches
Introduction
The collection of biological data for fish and other marine organisms are essential for many aspects of fisheries management including resource allocation, stock assessment, monitoring and evaluation of fish condition (including the development of indices), geographic comparisons of life histories and morphometrics (Ghosn et al., 2012; Goncalves et al., 1997; Lai and Helser, 2004; Mendes et al., 2004; Petrakis and Stergiou, 1995). Measurements of length (which may include total length, fork length, carapace length and shell width) and weight (which may include whole weight, gutted weight and wet weight) are biological metrics that make a valuable contribution to these aforementioned aspects of fisheries management, especially resource allocation, by enabling calculation of average weights for species of interest, either via conversion of length measurements from known length-weight equations or from direct measurement of weight. These metrics are also less demanding to collect accurately in terms of cost and time, and in conjunction with on-site boat ramp interviews, when compared to more intensive techniques required to determine age (otolith samples), or fecundity and maturity (gonad samples) of marine organisms.
Globally, in the commercial sector, it is often a licence requirement that fish are weighed on landing and fisheries observer programs may also provide an additional avenue for the collection of biological data (Hartill and Davey, 2015; Marriott et al., 2012; Stanley et al., 2009). Similarly, charter operators within the recreational sector in some countries also have a mandatory licence requirement to submit logbooks containing data on fish length and/or weight as well as information on catch and effort (Chan et al., 2018; Gray and Kennelly, 2017; Hartill et al., 2012). Conversely, recreational fisheries are predominately open access with no mandatory reporting requirements and are undertaken in diverse environments with multiple, diffuse access points. Establishing a survey design which allows representative samples of length and weight to be collected can therefore be challenging, and requires significant resources and funding (Morato et al., 2001).
Depending on the objective of survey programs, biological data (including weight) are also collected during other fishery dependent and independent surveys, which may vary from one-off studies to long-term monitoring using a variety of techniques. Underwater visual census is also commonly used to estimate fish abundance and length, although it is difficult to obtain weight using this technique (Morey et al., 2003). However, depending on the spatial and temporal scales of such research, the average weight of species generated may not always be reliably applied to broader spatial areas or species distributions. For example, research may be focused on a small spatial area (i.e., river or estuary) or a small number of target species for small-scale fisheries (Brouwer and Buxton, 2002; Gray and Kennelly, 2003; Marriott et al., 2012; West and Gordon, 1994).
Length and weight data for recreational fisheries can be collected and verified by trained interviewers during on-site (i.e., boat ramp) surveys, which are generally utilised when a fishery is open access and are conducted over smaller spatial scales (Pollock et al., 1994). This differs from off-site surveys (i.e., phone/diary, mail) which are generally utilised for fisheries operating over broad-spatial scales or have a licence sampling frame and are designed to minimise potential errors, such as recall bias via regular telephone contact or use of a diary card (Henry and Lyle, 2003; Hyder et al., 2018; Ryan et al., 2016). Off-site surveys rely on self-reporting by recreational fishers and potential errors with reporting of length and weights (i.e., interpretation of different measurement instruments and rounding bias) (Bellanger and Levrel, 2017; Fairclough et al., 2014; Sparrevohn, 2013) can be mitigated by providing respondents with training material and measuring tools (i.e., calipers) (Bradford, 2000; Lyle et al., 2019). Volunteer programs, during which recreational fishers report their fishing activity in a logbook, or donate fish skeletons which are then utilised by researchers, can also be useful sources of biological data (Fairclough et al., 2014; Rocklin et al., 2014; Smith et al., 2007). Ensuring self-reported length and weight data is representative of the broader population is difficult due to the specific characteristics and behaviours of each fisher, although this effect can be minimised via randomisation and stratification.
The practicalities of collecting biological data from recreational fishers can also be challenging, especially when considering the additional burden on respondents (Georgeson et al., 2015; Hartill and Davey, 2015; Henry and Lyle, 2003). These include: time limitations (i.e., fishers are eager to depart a boat ramp); personal preference (i.e., fishers reluctant to have fish removed from storage) (Morales-Nin et al., 2005); difficulty in setting up scales in exposed environments (i.e., need to be on a level surface for accurate reading); and transporting equipment to remote locations to access fishers (i.e., scales may be bulky and sensitive to knocks). Recreational fishers may also be suspicious that length information will be used to report non-compliance with slot limits. For these reasons, as well as others relating to the practicality of weighing large fish which are often released, collection of biological data has been excluded from many surveys, or only estimated based on a visual inspection of the catch (Ghosn et al., 2012; Herfaut et al., 2013; Rangel and Erzini, 2007).
If average weight data are not available for a particular species or time period, this information may instead be acquired from secondary sources or imputed from random length samples. These data may be for the same species but from different stock distributions, sectors (i.e., commercial or charter), jurisdictions or an earlier sampling period (Hamer et al., 2019; Lloret et al., 2008; Ma and Ogawa, 2016; Radford et al., 2018; Strehlow et al., 2012; Tracey et al., 2020, 2013; Veiga et al., 2010). Although length data are generally easier to collect (i.e. a measuring tape or mat is more transportable), obtaining such measurements may only be secondary after asking questions relating to primary objectives of fishing effort and total catch. Furthermore, length-weight relationships are still then required to impute weight from measured length, and are often only known for the most common and frequently studied species (Torres et al., 2012). Such approaches may produce estimates of average weight that are not representative (Henry and Lyle, 2003; Lyle et al., 2009; Ryan et al., 2016).
Exploring differences in on-site survey designs may provide opportunities to improve the collection of weight data from recreational fishers. Randomised survey designs use probability-based sampling regimes to collect data across broad spatial and temporal strata, which are often defined by periods of similar activity levels to improve the variance of estimates when expanding to a population (Pollock et al., 1994). It may be difficult to obtain measurements when sampling during periods of low activity (i.e., winter months), due to low survey effort and few interviews being completed. Conversely, a probability-based randomised survey which is restricted to spatial and temporal periods of peak fishing activity (herein referred to as a restricted survey) are more likely to obtain greater numbers of interviews (MRIP Design and Analysis Workgroup, 2012); although this may influence the representativeness of data, as the biological and behavioural characteristics of fish and fishers may change temporally (Al Nahdi et al., 2016; Hartill and Davey, 2015). Considering the differences in survey designs, and the implications this may have on data, is important to ensure comparability between surveys, and over the long-term.
This paper investigates randomised and restricted survey designs and their ability to collect length and weight data from finfish and invertebrates caught by boat-based recreational fishers. These data are essential for converting estimates of recreational catch (by numbers) to catch (by weight) and can also be developed into an index of recreational catch to monitor change over time (similar to catch rate indices). Implementing recreational fishing surveys with the specific aim of obtaining data on average weight for this sector is rare, as is the use of a restricted spatial and temporal survey design. The two designs are evaluated in terms of survey effort, species composition and cost-effectiveness of the survey designs as well as average weight and relative precision of estimates for individual species. The findings from this study will assist with the development of an index of average weight, provide more timely and accurate catch estimates (by weight) for recreational fisheries and improve the efficiency of survey designs for the collection of weight data from the recreational sector. This, in turn, will benefit fisheries management policies, particularly those that allocate resources across sectors.
Section snippets
Study Area
In Western Australia, the coastline extends 12,889 km and recreational fishing is widespread across four broad marine bioregions from the tropical north to the temperate south (Fig. 1). These waters contain approximately 3,000 fish species (Hutchins, 2001), of which ∼10% are harvested by recreational fishers. However, a small number of these species contribute a large proportion of the recreational catch. For example, Glaucosoma hebraicum, Chrysophrys auratus, Choerodon rubescens and
Survey Effort
The restricted survey design in 2013/14 had the desired effect of providing greater survey hours in the North Coast, Gascoyne Coast and South Coast when compared to 2011/12 (Table 2). Statewide, 41% of survey hours in 2011/12 were undertaken in the 4-month peak fishing season corresponding to the 2013/14 survey, with the North Coast having the highest proportion (50%).
As expected from the increased number of survey hours (which is the amount of time which was spent by the interviewer at each
Discussion
Worldwide, robust estimates of recreational catch (by weight) are essential for facilitating the equitable allocation of catch between sectors and are an important element of sustainable fisheries management (Crowe et al., 2013; Hyder et al., 2018; Ryan et al., 2016). The dispersed nature of recreational fisheries, which are often characterised by numerous access points, means that collecting weight measurements from this sector is challenging. However, without such information it is not
Conclusion
The randomised and restricted Boat Ramp Surveys were both successful in achieving their objective of obtaining biological data on length and weight for key species caught by boat-based recreational fishers. Although the restricted survey sampled only peak activity periods, this design performed better when evaluated with respect to survey effort, species composition, cost-effectiveness and relative precision of average weights, especially for demersal species. These benefits were readily
CRediT authorship contribution statement
Claire B. Smallwood: Methodology, Project administration, Formal analysis, Writing - original draft. Karina L. Ryan: Conceptualization, Methodology, Project administration, Writing - review & editing.
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgements
This study would not be possible without contributions from the many recreational fishers who took the time to participate in the boat ramps interviews throughout Western Australia. Thanks also to the Research Survey Officers and Technical Officers who conducted all the fieldwork. Stuart Blight, Vangie Gerginis, Tim Leary, Elena Sulin, Adrian Thomson, Veronique Vanderklift, Karen Williams and Brent Wise from the Department of Primary Industries and Regional Development (formerly Department of
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