Do risk-prone behaviours compromise reproduction and increase vulnerability of fish aggregations exposed to fishing?
Data files
Aug 05, 2024 version files 143.56 KB
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BS_livecoral.csv
758 B
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BS_structure.csv
1.44 KB
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FID.csv
6.39 KB
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focal_context.csv
28.26 KB
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popcen.csv
39.31 KB
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README.md
9.57 KB
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timebudgets.csv
57.84 KB
Abstract
Human disturbances can prompt natural antipredator behaviours in animals, affecting how energy is traded-off between immediate survival and reproduction. In our study of male squaretail groupers (Plectropomus areolatus) in India's Lakshadweep archipelago, we investigated the impact of fishing pressure on anti-predatory responses and reproductive behaviours by comparing a fished and unfished spawning aggregation site and tracking responses over time at the fished site. Using observational sampling and predator exposure experiments, we analysed fear responses (flight initiation distance, return time), as well as time spent in vigilance, courtship, and territorial defence. Unpaired males at fished sites were twice as likely to flee from simulated predators and took longer to return to mating territories. Contrastingly, males in the presence of females at both sites took greater risks during courtship, fleeing later than unpaired males, but paired males at the unfished site returned earlier. Our findings suggest that high fishing pressure reduces reproductive opportunities by increasing vigilance and compromising territorial defence, potentially affecting mate selection cues. Altered behavioural trade-offs may mitigate short-term capture risk but endanger long-term population survival through altered reproductive investment. Human extractive practices targeting reproductive aggregations can have disruptive effects beyond direct removal, influencing behaviours crucial for population survival.
README: Do risk-prone behaviours compromise reproduction and increase vulnerability of fish aggregations exposed to fishing?
https://doi.org/10.5061/dryad.ncjsxkt33
Description of the data and file structure
The dataset consists of 6 data files:
FID.csv: This dataset contains estimates of reactive anti-predatory responses in male squaretail groupers based on experimental manipulation of predation risk (i.e, predator simulation). Estimates of flight initiation distance (FID) and return times of 117 males from the fished and unfished aggregation site. Also includes Information on courtship status of male (paired, unpaired), body size. File used to generate Figure 1.
Metadata description:
Date (DD/MM/YYYY): Date the focal observations were made.
Island: Name of the Island of the squaretail grouper aggregation site.
ID (numeric): Unique Identification number given to a focal individual.
size (cm) : Total body size (cm) of the focal individual (tip of the snout to edge of caudal fin). Empty cells indicate data not available.
sex (male/female): Whether male or female. Empty cells indicate data not available.
habitat (slope/shelf): Whether focal territory was located on the slope or the shelf of the aggregation site. Empty cells indicate data not available
FID (metres): Flight Initiation Distance (meters). The distance between the observer and focal individual, when it attempts to move away from the observer. Empty cells indicate data not available
return_time (seconds): The time taken (seconds) for the disturbed focal individual to return to it's territory after the observer moves away. Empty cells indicate data not available
mates (number): Number of squaretail groupers in a 25meter squared area (5 meter radius) around the focal individual's territory. Empty cells indicate data not available.
mates_cat(no/yes): Whether mates were present or not in the immediate vicinity of focal individual. Empty cells indicate data not applicable.
female_size (cm): If mates were females, what was the total body size (cm) of females. Empty cells indicate data not applicable.
male_size (cm): If mates were males, what was the total body size (cm) of males. Empty cells indicate data not applicable.
timebudgets.csv: This dataset contains proactive anti-predatory responses, i.e time activity budgets (the proportion of time in vigilance, courtship and aggression behaviours) from 71 focal males in the fished and unfished sites (sampled in 2023/24) and 31 individuals sampled at the fished site in 2013/14 (i.e in a pre-fishing condition). File used to generate Figure 2.
Metadata description:
island: Name of island of aggregation site, fished (Bitra), unfished (Site_2)
date (DD/MM/YYYY): Date of focal observation
video.id (xyz.MVI): File name of associated focal video
id (1,2,3...): Unique Identification number given to a focal individual.
time.start (mm:ss): Start time (minutes) of a behavioural observations.
time.end (mm:ss): End time (minutes) of a behavioural observations.
duration (seconds): Total duration of a behavioural observation.
state: Broad behavioural state of the focal individual (vigilance, courtship or aggression, defined in Electronic supplementary material 2, table 1).
substate: Specific behaviours associated with the behavioural state (described in Electronic supplementary material 2, table 1).
substate2: additional details associated with substate
colour: body colour of focal individual (brown mottled, striped, dark spotted, pale spotted, two tone).
event: instantaneous response of the focal individual to an interaction with a competitor or mate. Empty cells indicate n/a not applicable because event was not observed
no.interactors (#): number of individuals the focal individual interacted with. Empty cells indicate n/a data not applicable.
interactor.size (cm): Total body size (top of snout to edge of caudal fin) of interacting individuals (whether larger, smaller or of equal size to focal individual). Empty cells indicate n/a data not applicable.
outcome: outcome of interactions for the focal individual. Empty cells indicate n/a data not applicable.
habitat: dominant substrate of where interaction took place. Empty cells indicate n/a data not applicable.
notes: additional descriptive observations of the interactions. Empty cells indicate n/a data not applicable.
focal_context.csv: This dataset is linked to timebudgets and is combined into a single dataset in the code manuscript_figures.RMD. Contains contextual information of focal individuals at the time of sampling, in terms of body size, individual social context (number of mates and competitors in immediate vicinity), habitat etc. File used in GLM analysis of drivers of behaviours.
Metadata description:
date:(DD/MM/YYYY): Date of focal observation.
day (Peak, Peak-1,Peak+1...): Number of days before and after the Peak spawning day (i.e, New Moon night).
island: Name of island of aggregation site, fished (Bitra), unfished (Site_2).
video_id (name): name of associated video file.
video.length:(mm:ss): Total length (minutes: seconds) of the video.
focal_id (1,2,3...): Unique identification number of focal individual.
sex (M/F,U): Whether focal individual is male , female or unknown. Empty cells indicate data is not available.
size (cm): Total body size (cm) of the focal individual (tip of the snout to edge of caudal fin). Empty cells indicate data is not available.
habitat: Habitat type of focal individual (slope, shelf, sand). Empty cells indicate data is not available.
live_coral (score: 0-5): Live coral cover visually scored between 0-5, where 1 is bare platform and 5 is 100% coral cover in a 1x1 meter squared digital photoquadrat (see electronic supplementary material 2, table2 for details).Empty cells indicate data is not available.
structurescore: 0-5: Structural complexity (vertical coral canopy height) scored between 0-5 with 0 as lowest and 5 as highest (see electronic supplementary material 2, table2 for details).Empty cells indicate data is not available.
sand (score: 0-5): Percentage cover of sand visually scored between 0-5 with 0=0% to 5=100%. Empty cells indicate data is not available.
neighbour size (cm): Total body size (cm) of neighbouring individuals. Empty cells indicate data is not applicable.
neighbour(#): Number of neighbours in the immediate vicinity (5meter radius) of focal individuals. Empty cells indicate data is not available.
predators (species name, #). Empty cells indicate data is not available.
notes: additional descriptive observations of the focal individual interactions.
popcen.csv: This dataset contains estimates of population census of the squaretail grouper aggregation conducted using 5-7, permanent belt transects (50 x 10m) established at the fished (Bitra) site since 2013 and unfished (Site_2) site since 2021,respectively. Observations are conducted over 3-5 days days during the new moon lunar phase in January, February and March each year. Dataset used to generate Table 1 and figures in electronic supplementary material 1 and 2.
Metadata description:
Date (DD/MM/YYYY): Date the focal observations were made.
Year (YYYY): Year of annual survey.
Island: Name of the Island of the squaretail grouper aggregation site (Bitra, Site_2).
Month: Month of survey (Jan, Feb, March).
Transect.no: (1-7) ID of 50 x 10m belt transect.
sex: Whether grouper individuals were M (male), F (female) or U(unknown). Empty cells indicate data is not available.
size (cm): Total body size (cm) of the male (tip of the snout to edge of caudal fin). Empty cells indicate data is not available.
Depth (metres): Average depth of the belt transect.
Zone: Broad reef zone of the belt transect (crest, slope, shelf, sand).
lunar.day: days since peak spawning (i.e, since the new moon day). Empty cells indicate data is not available.
tot.abun (#): total number of individuals of a particular size and sex.
BS_livecoral.csv: Live coral cover visually estimated from photographs of 1m.squared quadrats (n=5) in three belt transects (50 x 10m) at the fished and unfished site. Data used in Table 1. Empty cells indicate data not available.
Metadata description:
Date: (DD/MM/YYYY): Date of focal observation.
island: Name of island of aggregation site, fished (Bitra), unfished (Site_2).
transect (1-3): ID of 50 x 10m belt transect.
Quadrat (1-5): ID of 1x1meter quadrat placed every 5m along each transect.
percentage_lc (%): Percentage cover of live coral in the quadrat.
percentage_sand (%): Percentage cover of live coral in the quadrat.
BS_structural complexity.csv: Vertical canopy height (meters) estimated in-situ, n=10 measurements on three belt transects (50 x 10m) at the fished and unfished site. Data used in Table 1. Empty cells indicate data not available.
Metadata description:
date:(DD/MM/YYYY): Date of focal observation.
island: Name of island of aggregation site, fished (Bitra), unfished (Site_2).
transect_no (1-3): ID of 50 x 10m belt transect.
depth_cm (cm): 10 random vertical height measurements taken within each transect.
Code/Software
manuscript_figrues.Rmd: R code for the analysis and production of Figures in MS.
ESM.Rmd: R code for reproducing figures and data used in Electronic Supplementary Material
Notes
run manuscript_figures.Rmd before ESM.Rmd as many objects are called in ESM
Methods
Refer to paper and Supplementary Materials (ESM)
Methods
2.1.Field sites
Data were collected from a ‘fished’ squaretail grouper spawning aggregation site (Bitra) during the new moon phase in January and from an ‘unfished’ site (Site 2) in February 2023 and 2024, in the Lakshadweep archipelago (details in electronic supplementary material 1, site characteristics). Historical data wasere also used from the fished site from January 2013 and 2014 (i.e., when it was in an ‘’unfished’ state, [20]). Sampling, site and aggregation characteristics are summariszed in table 1. Two prominent modes of active in-water reef fishing were observed at the fished site: hook-and-line and spearfishing, both involveing fishers free-diving in the water (RK, personal observation, details in ESM, electronic supplementary material 1). Anti-predator behavioural responses have been demonstrated in response to both fishing scenarios [16,17,21].
2.2.Squaretail grouper spawning aggregations
Squaretail groupers aggregate at both study sites for 5–6 days around the new moon from December to March [20]. Male groupers arrive 2–3 days earlier, establishing temporary territories (5–15 m2) that are vigorously defended from neighbours. Females typically join a day before the new moon and stay for 2–3 days after. The mating system is described as a ‘'lek’' [20]. Given the males’' stationary behaviour and distinct body markings facilitating easy identification, our study focussed on analysing male reproductive behaviours.
2.3.Population surveys
The total aggregation area, including the ‘'core’' lekking zone, was marked during snorkel surveys (refer to [20] and electronic supplementary material 1, for methods). Groupers were surveyed within this core area by two observers (RK, IMK) using underwater visual sampling on SCUBA along permanent 50 mx× 10 m belt transects. The number of transects varied based on the core area size (n = 5 fished site, n = 7 unfished site). Abundance estimates per transect were used to calculate average site-level population density (grouper.500 m−2). Observers also recorded fish lengths (5 -cm bins) and sex in situin situ [20]. Habitat characteristics such as structural complexity and percentage of live coral cover were assessed along three 50 -metre transects at the sites (details in electronic supplementary material 2).
2.4.Behavioural observations
Males were ‘paired’ with a female, if females were observed within male territories during focal follows and if displaying ‘'mate-guarding’' behaviours, such as maintaining close contact with females or hovering nearby (electronic supplementary material 2: table S1).
(i) Reactive response:
Reactive responses were measured at the fished and unfished sites during surveys done in 2023–2024. To determine the reactive fear response in territorial male groupers, we used ‘Flight Initiation Distance (FID)’, i.e., the distance at which the focal animal moves to avoid an approaching human observer [22]. FID is commonly used as an indicator to test for fish wariness in response to fishing [16]. We simulated predation risk by horizontally approaching, opportunistically selected territorial males (n = 72) on SCUBA at a steady pace from a standardiszed distance of five5 metres [23]. The approaching observer dropped a marker when the male began to move away and the linear distance between the grouper position (prior to movement), and the marker was measured by a second observer with a tape measure. Time away from territory is known to positively influence territory intrusion in spawning territorial damselfish [24]. Therefore, we retreated five5 metres from the male territory, immediately after the simulated disturbance to record how quickly an individual returns to its territory. In a pilot assessment of 20 males, over 70% of males returned within a minute, suggesting that immediate responses were critical for territory holders. We therefore used 120 secondsec as a cut-off time in our extended dataset.
(ii) Proactive response:
Focal video sampling was used to estimate timed-activity budgets, comparing behaviour among the fished and unfished sites in 2023–2024, and within the fished site in 2013–2014 &and 2023–2024. Observations were conducted on 108 territorial males over three days at each site, encompassing a day before, during, and after the new moon. Male behaviours were categoriszed into three states: ‘'courtship’' (male-–female interactions), ‘'territorial aggression’' (male-–male interactions), and ‘'vigilance’' (electronic supplementary material 2: table S1). The proportion of time spent in each activity was calculated by dividing the total time in different states (seconds) by the total video length (seconds).
To determine whether fishing rather than site-level population and environmental factors drove time activity budgets, we collected information on focal male body size (cm) and the number of males and females in an area of 25 m2 (i.e., competitor and mate density) from the centre of focal male territories. Habitat condition (live coral cover) and habitat structure (structural complexity) were ranked on a scale of 0–5 for each territory (electronic supplementary material 2,: table S2), owing to their influence on anti-predator behaviours like shelter-seeking [25,26] and predator avoidance [27]. Context data were not available for the historical dataset (2013-–2014), which was excluded from the analysis of drivers.
Statistical analysis
(i) Reactive response:
We used bootstrap resampling (R = 1000) to generate 95% confidence intervals to compare mean Flight Initiation Distance (FID) and territory return times between paired and unpaired males at fished and unfished sites. Non-overlapping confidence intervals indicated significant differences [28]. Proactive response: We also employed bootstrap resampling to compare activity budgets between paired and unpaired males at fished and unfished sites and within the fished site (2013–2014 pre-fishing and 2023–2024 fishing scenario). Ternary plots illustrated trade-offs between courtship, aggression, and vigilance.
(ii) Drivers of activity budgets:
Bayesian Zero-and-One Inflated Dirichlet (zoid) regressions [29] were used to model the influence of fishing status, habitat condition, male size, and social context on time activity budgets. The analysis involved 70 individuals surveyed in 2023–2024. All analysis was conducted in R (electronic supplementary material 3,: Table 4table S4).