Tide, time and space: Scales of variation and influences on structuring and sampling beach clams

Gray, Charles A.

doi:10.1016/j.jembe.2015.09.013

Cited by 14 publications

(8 citation statements)

References 50 publications

(86 reference statements)

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“…Moreover, the components of variation were consistently greatest across the smallest spatial scale sampled; among replicate samples taken at each site on each day and they were also generally high for the factors Site and Day. These results exemplify the need for future assessments of beach clams to adequately account for small-scale variability in sampling strategies to avoid potential confounding of larger scale comparisons [ 33 ]. Small-scale spatial and temporal variability is not uncommon in benthic assemblages [ 41 – 43 ] and was expected; previous sampling over a hierarchy of scales identified that variability in the densities of clams was consistently greatest across the smallest spatial and temporal scales examined [ 33 ].…”

Section: Discussionmentioning

confidence: 92%

“…Clams were sampled across two habitats, the swash zone and the dry sand belt typically located between 10 and 30 m above the low-tide swash zone level on each beach. To account for small-scale temporal and spatial variability [ 33 ], in each of the three periods sampling was done across two randomly selected days in each of three randomly selected weeks, except for the swash habitat in Period 1 when only four days (two weeks) were sampled. On each sampling day, eight sites in the swash zone and another eight sights in the identified clam belt in the dry sand were selected at random on each beach, and at each of these locations, six replicate samples were taken [ 27 ].…”

Section: Methodsmentioning

confidence: 99%

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Effects of Fishing and Fishing Closures on Beach Clams: Experimental Evaluation across Commercially Fished and Non-Fished Beaches before and during Harvesting

Gray¹

2016

PLoS ONE

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Management responses to reconcile declining fisheries typically include closed areas and times to fishing. This study evaluated this strategy for a beach clam fishery by testing the hypothesis that changes in the densities and size compositions of clams from before to during harvesting would differ between commercially fished and non-fished beaches. Sampling was spatially stratified across the swash and dry sand habitats on each of two commercially fished and two non-fished beaches, and temporally stratified across three six-week blocks: before, early and late harvesting. Small-scale spatio-temporal variability in the densities and sizes of clams was prevalent across both habitats and the components of variation were generally greatest at the lowest levels examined. Despite this, differences in the densities and sizes of clams among individual beaches were evident, but there were few significant differences across the commercially fished versus non-fished beaches from before to during harvesting. There was no evidence of reduced densities or truncated size compositions of clams on fished compared to non-fished beaches, contrasting reports of some other organisms in protected areas. This was probably due to a combination of factors, including the current levels of commercial harvests, the movements and other local-scale responses of clams to ecological processes acting independently across individual beaches. The results identify the difficulties in detecting fishing-related impacts against inherent levels of variability in clam populations. Nevertheless, continued experimental studies that test alternate management arrangements may help refine and determine the most suitable strategies for the sustainable harvesting of beach clams, ultimately enhancing the management of sandy beaches.

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Section: Discussionmentioning

confidence: 92%

Section: Methodsmentioning

confidence: 99%

Effects of Fishing and Fishing Closures on Beach Clams: Experimental Evaluation across Commercially Fished and Non-Fished Beaches before and during Harvesting

Gray¹

2016

PLoS ONE

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“…Swash zone sampling in Gray et al (2014) and in Ferguson et al (2015) was performed at low tide. Gray et al (2016a) explained that low tide ±3 h was convenient for driving along beaches to access sampling locations. Totterman (2019b) raised concerns that Gray’s (2016b, 2016c) counts were biased by seasonal changes in low tide zonation of D. deltoides .…”

Section: Discussionmentioning

confidence: 99%

A “feet digging” swash zone sampling method for the sandy beach bivalveDonax deltoides(Bivalvia: Donacidae)

Totterman

2019

Preprint

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6A "feet digging" method for sampling the sandy beach bivalve Donax deltoides was evaluated by 7 comparison to quadrat-based results from eleven beaches in subtropical eastern Australia. The method was 8 developed from a recreational fishing technique that involves twisting one's feet into the thixotropic sand to 9 dislodge buried clams which are then recovered by hand. Several plots are sampled across the swash zone in 1 0 one five-minute sampling unit and the process is replicated at several locations along the beach. Mean feet 1 1 digging clam counts were proportional to mean transect linear clam densities (r = 0.98). Clam length-1 2 frequency distributions from feet digging were similar to those from quadrat sampling except that feet 1 3 digging was not effective for clams < 16 mm. Feet digging counts are sensitive to both across shore (tidal) 1 4 and alongshore variation in clam abundance and were less precise than those from quadrat-based methods 1 5 (CV 1.2× larger). However, feet digging is fast and the method should be useful for low cost surveys of 1 6 Donax deltoides and similar "surf clams". 1 7

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“…Clams are spatially structured species, patchily distributed in their living area (McLachlan et al 1996;Dugan and McLachlan 1999;Defeo 2003;Denadai et al 2005) and this pattern makes them challenging to sample (Gray 2016). Formers monitoring programs results in Arcachon bay confirm the patchy spatial structure of manila clams in this area, but also highlight a temporal variation of abundance and biomass between both campaigns (Sanchez et al 2014).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Optimizing cost-efficiency of long term monitoring programs by using spatially balanced sampling designs: The case of manila clams in Arcachon bay

Kermorvant

Caill-Milly

Bru

et al. 2019

Ecological Informatics

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Funding lake is one major issue in ecology, in particular at local scale. It is known that sustainable management of a natural population requires a good understanding of its functioning, itself dependent on a good long term monitoring program. Such programs are usually very difficult to implement, especially for resources characterized by high spatio-temporal variation in their distribution, resulting in a trade off between efficiency and costs. Today, thanks to rapidly evolving statistical theory, new survey designs are developed, some with the characteristic of well balancing samples in the study area. This paper aims at demonstrating that theses advanced sampling designs perform better than the usual ones for long term monitoring program of local resources, with the added benefices of saving money and also increasing results accuracy. To prove it, and for it high spatio-temporal variation in it distribution, we choose the example of Manila clam's stock monitoring in Arcachon bay. This stock is under high scrutiny and last campaigns could not be done because of lack of funding (at least 50,000€/survey). We use a simulation study based on real data to assess and compare performances of news and older sampling designs on this survey. Three sampling designs are tested in both of the 6 past monitoring campaigns data and we estimate the cost of their application in the field. Selected sampling designs are: 1-simple random sampling (SRS-the one used in the past years of this monitoring program), 2generalized tessellation sampling (GRTS-a recent spatially balanced sampling design known for its high performance) and, 3-balanced acceptance sampling design (BAS-a newly developed spatially balanced sampling design, never tested yet in a real population). We first confirm that the two spatially balanced sampling designs perform better than simple random sampling. Both of the advanced sampling designs perform equally and allow achieving same accuracy in the results with almost half sampling intensity than SRS. This makes them so cost-effective that 30% of each campaign price could be saved if they were used. Moreover, the three sampling designs need a constant sample size thought years to achieve a fixed accuracy in results. This will permit us to fix one sample size that could be done for all future campaigns; and this, despite the existence of spatial and temporal variations in clam's distribution. Highlights ► Long term monitoring program at local scale are mandatory for resource management but often too expensive to undertake. ► For the example of manila clams resource in Arcachon bay, each campaign price can be lowered by 30% only in using spatially balanced sampling design instead of simple random sampling. ► More than lowering the survey price, wanted accuracy in the results can be fixed a priori. ► BAS sampling design, never compared to other sampling designs in real data previously perform very well.

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Tide, time and space: Scales of variation and influences on structuring and sampling beach clams

Cited by 14 publications

References 50 publications

Effects of Fishing and Fishing Closures on Beach Clams: Experimental Evaluation across Commercially Fished and Non-Fished Beaches before and during Harvesting

Effects of Fishing and Fishing Closures on Beach Clams: Experimental Evaluation across Commercially Fished and Non-Fished Beaches before and during Harvesting

A “feet digging” swash zone sampling method for the sandy beach bivalveDonax deltoides(Bivalvia: Donacidae)

Optimizing cost-efficiency of long term monitoring programs by using spatially balanced sampling designs: The case of manila clams in Arcachon bay

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