Are bull sharks endangered or threatened?
Author
Ray Brown
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Topic: Are bull sharks endangered or threatened?
May need another ITP if so.
Bulls of the Pamlico!
Shrimp trawling never stops in Pamlico Sound. It just pauses on the weekend so crabs can remove the dead and dying from the battlefield.
Bread Man 1
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Bunch of garbage in that article if you ask me. The "experts" claiming that bull sharks are a new occurrence in Pamlico Sound is laughable at best.
bakesta
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The manuscript was obviously not reviewed by the DMF or NCFA. Therefore, it is not permitted to claim that the Pamlico Sound is a nursery area for anything.
DMF scientists/directors have long said that extrapolations like that are just not permitted in marine fisheries management. How dare those authors call our pamlico sound a nursery area!
And didn't the republicans of NC outlaw the term global warming?
This paper just offends at every level (if you are an idiot).
"Do the right thing. It will gratify some people and astonish the rest." --- Mark Twain
Ray Brown
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According to the article the science was developed by the DMF. But that is consistent with our history. The regulatory wing of the DMF often disagrees or ignores the findings of DMF scientists. Been doing it for years.
Shrimp trawling never stops in Pamlico Sound. It just pauses on the weekend so crabs can remove the dead and dying from the battlefield.
Rick
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link to the scientific paper-
Increased Abundance and Nursery Habitat Use of the Bull Shark (Carcharhinus leucas ) in Response to a Changing Environment in a Warm-Temperate Estuary Charles W. Bangley ORCID: orcid.org/0000-0002-6044-7694 1 < ="East Carolina University" itemprop="name">< ="0000 0001 2191 0423, grid.255364.3, Institute for Coastal Science and Policy, East Carolina University, East 5th St, Greenville, North Carolina, 27858, USA" itemprop="address"> , 4 < ="Smithsonian Environmental Research Center" itemprop="name">< ="0000 0000 8612 0361, grid.419533.9, Fish and Invertebrate Ecology Laboratory, Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, Maryland, 21037, USA" itemprop="address"> Lee Paramore 2 < ="North Carolina Division of Marine Fisheries, Manteo Field Office" itemprop="name">< ="North Carolina Division of Marine Fisheries, Manteo Field Office, 1021 Driftwood Drive, Manteo, North Carolina, 27954, USA" itemprop="address"> David S. Shiffman 3 < ="Simon Fraser University, 8888 University Drive" itemprop="name">< ="0000 0004 1936 7494, grid.61971.38, Earth to Oceans Group, Department of Biological Sciences, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada" itemprop="address"> […] Roger A. Rulifson 1 < ="East Carolina University" itemprop="name">< ="0000 0001 2191 0423, grid.255364.3, Institute for Coastal Science and Policy, East Carolina University, East 5th St, Greenville, North Carolina, 27858, USA" itemprop="address"> - Show fewer authors Scientific Reports volume 86018 (2018 ) doi :10.1038/s41598-018-24510-z Download Citation Received: 25 October 2017 Accepted: 15 March 2018 Published online: 16 April 2018 Abstract
A general northward shift in marine species distributions has been observed in the western North Atlantic Ocean, which may have significant ecological consequences. Large coastal sharks can have wide migratory distributions but show fidelity to specific nursery habitats. Here we show evidence for nursery range expansion into Pamlico Sound, North Carolina by a marine apex predator, the Bull Shark (Carcharhinus leucas ). Previous assessments have shown little to no use of estuarine North Carolina waters as nursery habitat by Bull Sharks from 1965–2011. Juvenile sharks were rarely captured in a fishery-independent gillnet survey conducted by the North Carolina Division of Marine Fisheries (NCDMF) from 2003–2011, but were present every year from 2011–2016. Juvenile Bull Shark presence in the Sound was strongly related to early summer temperatures and late summer salinities, which have increased in the estuary over the 13 survey years, and further evidence for increasing water temperatures in Pamlico Sound was found in a 45-year data set for the NCDMF estuarine trawl survey. These results suggest that increasing water temperature and salinity have allowed Bull Sharks to expand their nursery habitat. This shift will have unknown, but potentially strong, impacts on both the local ecosystem and interactions with humans.
Introduction
As ocean temperatures increase, marine taxa may shift their distributions poleward to remain within optimal temperature ranges1 , 2 3 , 4 5 , 6 7
Shifts in biodiversity can result in significant changes to local food web dynamics, ecosystem productivity, and even fisheries2 8 9 10
Many species of shark rely on shallow coastal or estuarine nursery areas during early life stages11 Carcharhinus leucas ) have been documented in the northern Gulf of Mexico12 , 13 , 14 , 15 16 , 17 18 , 19 , 20 20
Bull Shark nursery habitats tend to be located in areas with limited access to the ocean and highly variable salinity, often associated with barrier islands and narrow inlets12 , 14 , 15 , 17 , 21 , 22 23 20 , 24 25
Results
A total of 70 Bull Sharks were captured from 2003–2016 in the NCDMF gillnet survey. Based on known size-at-age ranges26
Bull Sharks in juvenile size classes were not consistently captured prior to 2011 but were captured in low numbers in 2004 and 2006 (Fig. 1a 1a 1b F = 9.576, p = 0.003, df = 1) and year (F = 6.423, p = 0.014, df = 1) (Supplementary Fig. S1 S1a
Catches of juvenile Bull Sharks were spatially distributed along the western shore of Pamlico Sound from the Long Shoal River to Rose Bay, and within the lower Neuse River (Fig. 2 2 F = 1.07, p = 0.301, df = 1) or longitude (F = 2.34, p = 0.126, df = 1) of survey stations.
Capture locations and total catch (N sharks) of juvenile Bull Sharks (Young-of-Year and Age 1+ combined) in sets from the North Carolina Division of Marine Fisheries (NCDMF) fishery-independent gillnet survey within Pamlico Sound. Data are from the 2003–2016 survey years. The polygon represents the border of the high catch area for juvenile Bull Sharks in the survey. Map created using ArcGIS 10.4 (ESRI, Inc. Redland, CA, USA http://desktop.arcgis.com/en/
Bull Sharks were captured across a range of environmental gradients. One-way ANOVA results showed significant differences in mean temperature and inlet distance between life stages (Table 1 1
Life Stage Depth (m) Temperature (°C) Salinity (ppt) Dissolved O2 (mg/L) SAV Distance (m) Inlet Distance (km) YOY 1.40 ± 0.57 27.94 ± 2.28 18.18 ± 4.00 6.81 ± 1.33 1201.23 ± 931.70 38.92 ± 4.96 Age 1+ 1.33 ± 0.51 29.44 ± 1.73 16.94 ± 4.27 6.52 ± 1.22 1175.05 ± 1135.54 41.90 ± 5.75 F 0.213 6.185 1.172 0.606 0.009 4.182 p 0.646 0.016 0.283 0.439 0.926 0.04
Table 1 Mean ( ± standard deviation) of environmental and spatial variables measured at stations where each Bull Shark life stage was captured by the NCDMF gillnet survey in Pamlico Sound, with ANOVA results (DF = 2) determining significant differences between life stages.
Because YOY and Age 1+ Bull Sharks could be distinguished based on environmental variables, generalized linear model (GLM) analysis was conducted on YOY and Age 1+ sharks independently, and on both age classes grouped together as Combined Juveniles. Inlet distance and year were dropped from both the whole sound and high catch area models due to collinearity with other variables. For the whole sound, the model with the lowest AICc value included all other variables. Only temperature and salinity were included in the final high catch area model, which had a lower AICc value than the whole sound model. Zero-inflated negative binomial-distributed GLM results showed that temperature and salinity had significant effects on CPUE for all age classes in both models (Table 2 2 S2
Whole Sound GLM Combined Juvenile YOY Age 1+ Variable CPUE Zero-Inflation CPUE Zero-Inflation CPUE Zero-Inflation Depth z 0.751 1.021 1.631 1.436 0.765 0.612 p 0.453 0.307 0.103 0.151 0.444 0.541 Temp z 3 .826 1.067 3 .124 1.812 3 .338 1.066 p <0 .001 0.286 0 .002 0.07 <0 .001 0.286 Sal z 6 .339 1.099 6 .767 3 .522 5 .656 0.98 p <0 .001 0.272 <0 .001 <0 .001 <0 .001 0.327 DO z −0.746 1.074 −672 −1.124 −0.52 0.017 p 0.455 0.283 0.501 0.901 0.603 0.986 SAV Dist z N/A −1.05 N/A −15.065 N/A −0.711 p N/A 0.294 N/A < 0.001 N/A 0.477 High Catch Area GLM Combined Juvenile YOY Age1+ Variable CPUE Zero-Inflation CPUE Zero-Inflation CPUE Zero-Inflation Temp z 2 .841 1.478 1.909 0.749 2 .561 1.134 p 0 .005 0.139 0.056 0.454 0 .01 0.257 Sal z 3 .394 1.608 4 .713 2.29 2 .897 1.617 p <0 .001 0.108 <0 .001 0.022 0 .003 0.106
Significant relationships (α = 0.05) are in bold. Temporal trends in environmental variables that were significantly related to Bull Shark CPUE varied by month (Fig.
3 , Table
3 ). Linear regression showed that temperature increased over 2003–2016 by approximately 0.08 °C/year in May, 0.06 °C/year in June, 0.03 °C/year in July, and 0.05 °C/year in September. Salinity increased over the same period by approximately 0.32 ppt/year in August and 0.17 ppt/year in September. The best-fitting relationships were temperature increases during May and June and salinity increases during August and September (Fig.
3 , Table
3 ).
Figure 3 From: Increased Abundance and Nursery Habitat Use of the Bull Shark ( Carcharhinus leucas ) in Response to a Changing Environment in a Warm-Temperate Estuary
Linear trends of May-September (months 5–9) (a ) water temperature (°C) and (b ) salinity (ppt) measurements by year recorded by the NCDMF fishery-independent gillnet survey. Data are from 2003–2016 survey years.
Click the link for the rest of the data and charts.
Discussion
To our knowledge, this study is the first to attempt to associate environmental factors with the apparent colonization of a nursery habitat by a marine apex predator. Our results provide strong evidence that an increase in the use of Pamlico Sound as a Bull Shark nursery is associated with changing environmental conditions in the estuary, with temperature as the likely primary driver of Bull Shark presence. Though Bull Sharks were a rare catch overall in NCDMF surveys, the number of juveniles captured in Pamlico Sound increased from six from 2003–2011 (average of 0.75 sharks per year) to 53 captured from 2011–2016 (average of 8.8 sharks per year) with a corresponding increase in CPUE. This represents a dramatic increase in juvenile Bull Shark presence from previous assessments of shark nursery habitat use in North Carolina waters20 , 24
We found that the increased CPUE of juvenile Bull Sharks was most strongly associated with increasing water temperatures and salinities, which occurred in early and late summer, respectively. These environmental changes were consistent between both gillnet and trawl survey data, suggesting that increasing early summer temperatures and late summer salinities have been consistent trends in this system. While salinity was highly variable year-to-year, the increasing trend in water temperature became more consistent in trawl survey data after 2008. Generally, water temperature influences both large-scale seasonal migration and finer-scale habitat selection in sharks, while salinity is more strongly associated with localized movements and habitat use27 17 13 17 17 , 28
In comparison with other areas of the U.S. Atlantic coast, northwestern Pamlico Sound represents the most likely nursery habitat north of the Indian River Lagoon based on the criteria of Heupel et al .11 18 16 , 17 17 19 , 24 , 29 25
The increase in juvenile Bull Shark abundance in Pamlico Sound coincides with a general northward shift in marine species distributions along the U.S. Atlantic coast4 , 30 , 31 Carcharias taurus ), has recently been observed using areas where it was historically rare as nursery habitat32 33 , 34 20 Negaprion brevirostris ) in Bimini35 20 36
Many wide-ranging large coastal sharks depend on specific regions or sites as nursery habitat37 3 8 38
Methods
Environmental and Bull Shark catch data from the North Carolina Division of Marine Fisheries (NCMDF) independent gillnet survey were analyzed for years 2003–2016. The gillnet survey has been conducted since 2001 but was expanded to include stations in the Neuse and Pamlico Rivers in 2003, so only data collected since 2003 were used to account for potential shark captures in lower salinities. The total study area for the gillnet survey ranged from Oregon Inlet to Portsmouth Island on the east side of Pamlico Sound and from Stumpy Point to Rose Bay on the western side, and included the estuarine portions of the Neuse, Pamlico, and Pungo Rivers (Fig. 5 ). The study area was divided into 1.85-km by 1.85-km cells, and sampling stations were selected by randomly choosing grid cells prior to sampling. The gillnet survey was conducted from February-December, and utilized a 219.46-m sink gillnet constructed of eight 27.43-m sections of 7.62-, 8.89-, 10.16-, 11.43-, 12.70-, 13.97-, 15.24-, and 16.51-cm stretched monofilament mesh soaked for 12 hours from sunset to sunrise. Sampling effort ranged from 487–645 sets per year (Supplementary Table S1 ). Depth (m), water temperature (°C), salinity (ppt), and dissolved oxygen (mg/L) were recorded at each sampling station, and distance from the station to the nearest inlet (inlet distance, km) and the nearest mapped submerged aquatic vegetation (SAV) bed (SAV distance, m) were measured using ArcGIS 10.1. SAV maps were generated using data from aerial and boat-based surveys conducted by the Albemarle-Pamlico National Estuarine Partnership (APNEP) 39 .
All sharks were identified to species, and sex and total length (TL, mm) were recorded. Bull Sharks were classified to life stages based on known total length at age estimates 26 , with sharks 500–810 mm TL classified as young-of-year (YOY), sharks 811–1400 mm TL classified as juveniles one year of age or older (Age 1+), sharks 1401–2000 mm TL classified as subadults, and sharks greater than 2000 mm TL classified as mature adults. Four sharks identified as Bull Sharks but with a recorded TL of less than 500 mm were assumed to be misidentified due to being less than minimum size at birth 24 and therefore were excluded from further analysis. One-way ANOVA was used to determine significant differences in the measured environmental and spatial variables between Bull Shark life stages, and life stages without any significant differences were combined for analysis.
Bull Shark catch per unit effort (CPUE) was standardized as sharks/set. Possible spatial changes in survey sampling effort were assessed by modeling latitude and longitude over year using Oneway ANOVA. Generalized linear models (GLMs) were used to determine whether year and any environmental or spatial variables were significantly related to Bull Shark CPUE during months when Bull Sharks were captured, and were set at a zero-inflated negative binomial distribution to account for zero-inflation, long-tailed distributions, and overdispersion common in ecological count data. To account for the potential for highly localized environmental variation, two GLMs were generated: one using data from the entire survey area and referred to as the whole sound model, and one only using data from survey sets falling within a polygon drawn around stations where juvenile Bull Sharks were captured and referred to as the high catch area model. In these models, a logit link function was used for the catch data and a log link for zero-inflation. Important environmental variables were identified based on significance ( p ) and effect size ( z -score). The best model was chosen by initially generating a model with all environmental variables, eliminating variables that would not resolve with the model, and then removing and re-adding the remaining variables in a stepwise fashion using the “step” function in R 40 . The model with the lowest corrected Akaike Correlation Criterion (AICc) was chosen to identify the environmental variables with a significant relationship with Bull Shark CPUE, and to predict CPUE based on those environmental variables. Potential changes over the study period in environmental variables identified as important by GLM results were assessed using linear regression to determine the significance of relationships between environmental measurements and year, during each month Bull Sharks were present.
Long term changes in environmental variables identified by annual trend analysis were assessed using data from the NCDMF fixed-station estuarine trawl survey within Pamlico Sound, which has been conducted annually since 1971 (Supplementary Fig. S3 ). Depth (m), temperature (°C), salinity (ppt), and dissolved oxygen (mg/L) concentration were recorded at each station. For environmental variables with a significant relationship with juvenile Bull Shark CPUE, linear bivariate ANOVAs were used to determine whether increasing or decreasing trends in those factors were significant over the 45-year period covered by the trawl survey. In addition, the percentage of early summer (May and June) temperatures greater than the minimum temperature at which Bull Sharks were captured in the gillnet survey was calculated for each year and trends were assessed using the same bivariate ANOVA procedure. To determine whether these longer-term changes may have influenced juvenile Bull Shark CPUE, the best GLM generated using the gillnet survey catches was used to predict CPUE based on environmental measurements recorded during the trawl survey. Predicted CPUE was plotted and compared visually with actual CPUE from the gillnet survey and environmental factors.
All statistical analyses were conducted using R statistical software version 3.3.1 40 .
Ethical Approval NCDMF is authorized by North Carolina state statute Article 20 § 113–261 to approve all sampling protocols internally. All field sampling procedures followed standard NCDMF-approved protocols.
Data Availability North Carolina public data are available through a public records custodian at the applicable agency according to North Carolina state statute (N.C.G.S § 132-2). All NCDMF fishery-independent survey data used in this manuscript can be accessed by contacting Lee Paramore (lee.paramore@ncdenr.gov) and submitting a Biological Data Tracking Form available at http://portal.ncdenr.org/c/document_library/get_file?uuid = 4c762326-de86-4661-a142-31c1d55e49bb&groupId = 38337 ).
fiogf49gjkf0d
NC Fisheries Management- Motto: Too Little, Too Late, Too Bad Slogan: Shrimp On! Mission Statement: Enable Commercial Fishing At Any and All Cost, Regardless of Impact to the Resource.
Bread Man 1
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And let's not forget that for years some DMF staff couldn't identify our 3 species of flounder. Who's to say they know what shark they are looking at?
kshivar
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Breadman that’s funny and sad at the same time. So true.
chriselk
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https://en.wikipedia.org/wiki/Nature_(journal)
The above comments are my personal opinion and do not represent those of any organizations or agencies I may be a member of.
Rick
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...a possible reason the bulls are showing up in greater quantities (they've always been there) is because the forge base feeding them is shrinking. Bycatch from trawling in the Pamlico is an attractant as the live forage base shrinks elsewhere.
...same goes for the sharks on the beach and the growing number of interactions with swimmers.
fiogf49gjkf0d
NC Fisheries Management- Motto: Too Little, Too Late, Too Bad Slogan: Shrimp On! Mission Statement: Enable Commercial Fishing At Any and All Cost, Regardless of Impact to the Resource.
todobien
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Looks like they are utilizing DMFs data and it is being accepted. Too bad DMF wouldn't accept your analysis of their data.
Rick
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todobien wrote:
Exactly
Paramore used-
Capture Rates from the- "independent gillnet survey conducted by the North Carolina Division of Marine Fisheries (NCDMF) from 2003–2011, but were present every year from 2011–2016"
Temperature Data from "evidence for increasing water temperatures in Pamlico Sound was found in a 45-year data set for the NCDMF estuarine trawl survey"
This statement from the shark study certainly supports my weakfish nursery area work based on similar analysis of abiotic variables that attract juvenile weakfish to the deeper more open areas of the sound.
The high catch area model was selected for use predicting CPUE (Whole sound model AICc = 445.78, high catch area model AICc = 412.57). Plots of juvenile Bull Shark CPUE against significant environmental variables suggested positive associations with temperatures greater than 22 °C and salinities between 10 and 25 ppt (Supplementary Fig. S2 ).
If Paramore can designate this broad polygon as the high catch area for juvenile Bull Sharks based his analysis of the Division's gillnet survey data
please explain why CPUE analysis using the Division's P195 Trawl Survey data doesn't support naming the deeper more open areas of the Pamlico Sound as weakfish primary nursery areas-
...and data certainly shows that the Division allows trawling in these undesignated primary nursery areas
fiogf49gjkf0d
NC Fisheries Management- Motto: Too Little, Too Late, Too Bad Slogan: Shrimp On! Mission Statement: Enable Commercial Fishing At Any and All Cost, Regardless of Impact to the Resource.
todobien
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Because they said so that's why
todobien
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Because it'd bring chaos into the fisheries management world if it was accepted. I wonder if the MFC scientist would be willing to take a look at it and see if it looks solid enough for the MFC to discuss and if warranted vote on whether to send to DMF to review and comment upon?????
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Topic: Are bull sharks endangered or threatened?
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todobien wrote:
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