Title of the dataset:
Data underlying the publication: "Spatial dependency in abundance of Queen conch, Aliger gigas, in the Caribbean, indicates the importance of surveying deep-water distributions"

Creators:
Erik M. Boman (a, b)* (ORCID: 0000-0003-1935-2682) 
Martin de Graaf (b)
Leopold A. J. Nagelkerke (a) (ORCID: 0000-0003-1130-749X)
Aad Smaal (a, b)
Ayumi Izioka-Kuramae (c)
Jimmy Van Rijn (b)
Melanie Meijer Zu Schlochtern (b)

a Aquaculture and Fisheries, Wageningen University & Research, Wageningen, The Netherlands
b Wageningen Marine Research, IJmuiden, The Netherlands

* Corresponding author at:
Aquaculture and Fisheries Group
Wageningen University & Research
P.O. Box 338
6700 AH Wageningen
The Netherlands
erik.b.boman@gmail.com 

Related publication:
Boman. E.M., de Graaf. M., Kough. A.S, Izioka-Kuramae. A., Zuur. A. F., Smaal. A., Nagelkerke. L.A.J. (2021). Spatial dependency in abundance of Queen conch, Aliger gigas, in the 
Caribbean, indicates the importance of surveying deep-water distributions. In: Diversity and Distibutions

Description:
Evaluate how the spatial distribution of a heavily exploited marine gastropod (i.e., Queen conch) varies in response to a number of known biotic and abiotic variables within and between 
sites that vary in environmental conditions. A novel towed video system complemented belt transects to estimate adult queen conch densities throughout its depth range. Bayesian 
hierarchical spatial models (Integrated Nested Laplace approximations) modeled distribution patterns of adult conch and indicated that the general patchy distribution pattern and the lack 
of strong generic location over-crossing relationships between abiotic and biotic factors and adult conch abundance and distribution is likely to at least partly due to this spatial 
dependency and location-specific factors, that affect different parts of the conch life-history.

Keywords:
Gastropod, INLA, Spatial correlation, Towed video, Population estimate
  
Spatial coverage:
Northern Caribbean (St Eustatius, Saba Bank, Anguilla)

Temporal coverage:
2011, 2013, 2014, 2015 

This dataset contains the following files:
1) Queen_conch_count_Boman2021.csv

Explanation of variables:
Location: ANG = Anguilla, STE = St Eustatius, SB = Saba Bank
Rock, Rubble, Sand, Reef = Abiotic substrate cover (total cover amount to 1) 
Algae, Seagrass = Biotic benthos cover (total cover can be < 1) 
Distance_open_Ocean_m = The distance of the sampling locatio in meters to the open ocean (and beyond depth limit of conch)
Depth_m = Average depth of survey transect
Density_Adult.ha = Adult Queen conch (Aliger gigas) density / ha
Count_adult_conch = Count of adult Queen conch (Aliger gigas) of each sample
Area_sampled_m2 = Sampled area in m2 per of each sample
Latitude : GPS in decimal degrees for the midpoint of the sample area
Longitude: GPS in decimal degrees for the midpoint of the sample area

Methods, materials and software:
1. Survey location
Surveys were conducted at three different sites in the Eastern Caribbean (Anguilla, St Eustatius [islands with narrow continental shelfs], and Saba Bank [offshore bank]), 
which differed in environmental variables (e.g., habitat homogeneity, geomorphology, waterflow patterns, depth). 

1.1 Anguilla
Survey transects (N = 132) were made between 31 August 2011 and 11 December 2015 in the waters around Anguilla, covering an area of approximately 940 km2 in depths of 3 to 54 m, 
with 48% of transects (N = 63) conducted in the peak breeding season (May-September). The area around Anguilla was divided in 5 × 5 km grid cells. Within each grid cell 5-6 survey 
transects were dispersed randomly (N = 117). In addition, within the survey area a total of 15 fixed transects for long-term monitoring of conch abundance in near shore shallow areas 
around Anguilla were added.  

1.2 St Eustatius
Survey transects (N = 167) were made in and in the close vicinity of the St Eustatius National Marine Park (0-30 m around the island) at depths of 6.5 to 45 m, between 11 June 2013 and 
5 March 2014, with ca 62% of transects (N = 103) made in the peak breeding season (May-September). Sampling locations in the waters surrounding St Eustatius 
were selected by a random sampling design. 

1.3 Saba Bank
Survey transects were made on the Saba Bank in depths of 16-57 m, between 9 April 2013 and 12 November 2014, with ca 42% of transects (N = 72) made in the peak breeding season 
(May-September). Sampling locations on the Saba Bank were assigned randomly inside a systematic grid (5 × 5 km cells) and 10 fixed locations monitoring 
long-term coral reef status along the Eastern edge of the bank. Due to the size of the Saba Bank (2200 km2) for practical reasons, three transects were towed in short distance of each 
other, separated by roughly 500 m.

2. Survey Method
Adult conch (defined here as conch with a fully developed lip) abundance was estimated using two comparable methods: towed video (Boman et al., 2016) and standard 
belt transects (CRFM, 2013). Belt transects, using scuba, were primarily conducted in high-relief habitats (mainly reef habitats) in which the towed video array was not suitable to use 
(Boman et al., 2016). Total adult conch counts for each transect were calculated for the purpose of modelling conch abundance and distribution patterns. Density (number of conch / ha) 
estimates for each transect were also calculated but only used as a comparative measure to previous surveys and not used for the models.

2.1 Towed video
Towed video transects at all three sites were conducted following Boman et al., (2016), with a transect width of 1 m and a transect length between 330-806 m. All adult conch inside the 
transects (i.e. more than 50% of shell inside the transect) were counted, and life status was determined based on visual cues (Boman et al., 2016). Substrate (sand, rubble, reef) and 
macrobenthos (algae, seagrass) cover were determined for each transect by analyzing 20 frames, with an equal spread in time over the transect. In each of the 20 frames, 10 set dots, 
in a 2 × 5 pattern, were overlaid and per dot, the underlying substrate and macrobenthos was identified. If a dot was blocked or the frame was blurry the next frame in which substrate 
and macrobenthos for each dot could be determined was used. Substrate and macrobenthos cover for each transect was calculated based on the average total of dot points from the 20 frames. 
A handheld GPS system was set to track the position, every 10 sec, to follow the transect and calculate transect length accurately. Mean depth (m) was also recorded for each transect and 
determined by the vessel’s depth sounder. 

2.2 Belt Transects   
Belt transects at each survey site were between 200-13900 m2, with 94% of the transects being between 200 – 1500 m2, and all adult conch within each transect were counted. Difference in 
transect area surveyed within sites was accounted for in the models by adding it as a log-transformed parametric covariate (Sampling effort). Life status was determined by visual 
inspection after turning over the animal. The divers estimated the percentage coverage of substrate (sand, rubble, reef) and macrobenthos (algae, seagrass) for each transect. The location 
of the transect were determined with a handheld GPS (Garmin GPSmap 78, Garmin Ltd., Olathe, KS, www. garmin.com). Mean depth was recorded for each transect as determined by the diver's 
computer. Measured substrate and benthos as well depth, distance to ocean, sampling effort, and Longitude and Latitude was used as covariates for the models.

References
Boman, E. M., De Graaf, M., Nagelkerke, L. A. J., Van Rijn, J., Meijer Zu Schloctern, M., & Smaal, A. (2016) Underwater towed video: a novel method to estimate densities of queen conch 
(Lobatus gigas; Strombidae) across its depth range. Journal of Shellfish Research, 35, 493−498.

CRFM. (2013). Underwater fisheries independent approaches for queen conch population estimation—a review. CRFM Technical and Advisory Document, No. 2013/14. 19 pp.


Information on data analysis and software can be found in the Related Publication (see above)
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E. Boman PhD (lead-author)
Aquaculture and Fisheries Group
Wageningen University & Research
P.O. Box 338
6700 AH Wageningen
The Netherlands
erik.b.boman@gmail.com 

This dataset is published under the CC BY-SA (Attribution - Share Alike) license.