Temporal trends in mortality and effects of by-catch on common bottlenose dolphins, Tursiops truncatus, in southern Brazil

The mortality of the bottlenose dolphin, Tursiops truncatus, on the southern portion of Rio Grande do Sul State coast was investigated based on 914 beach surveys conducted between 1969 and 2006. A total of 188 stranded bottlenose dolphins were recorded during this period, indicating a 1.8M:1F sex-ratio of those animals sexed (N = 79). Mortality was low in calves, high in juveniles and sub-adults and slightly lower than in adults. The overall mortality was clearly seasonal overlapping with higher fishing efforts in the Patos Lagoon Estuary and adjacent coastal areas, where most individuals washed ashore. Analysis of a continuous 14-year long subset (1993–2006) of the data indicated relatively low levels of mortality between 1995 and 2000 and a marked increase between 2002 and 2005 followed by an apparent drop in 2006. By-catch was responsible for at least 43% of the recorded mortality between 2002 and 2006. Juvenile males were more susceptible to incidental catches. Among females, by-catch of adults represented 75%. Results of a potential biological removal analysis suggest that current levels of fishing-related mortality are unsustainable for the small resident population of bottlenose dolphins that inhabits the Patos Lagoon Estuary, and that this population may be declining.

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Activity budgets and distribution of bottlenose dolphins (Tursiops truncatus) in the Patos Lagoon estuary, southern Brazil

Latin American Journal of Aquatic Mammals ◽

10.5597/lajam00121 ◽

2007 ◽

Vol 6 (2) ◽

Cited By ~ 10

Author(s):

P. H. Mattos ◽

L. Dalla Rosa ◽

P. F. Fruet

Keyword(s):

Tursiops Truncatus ◽

Bottlenose Dolphins ◽

Southern Brazil ◽

Activity Budgets ◽

Patos Lagoon ◽

Patos Lagoon Estuary

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Abundance of bottlenose dolphins, Tursiops truncatus (Cetacea: Delphinidae), inhabiting the Patos Lagoon estuary, southern Brazil: implications for conservation

Zoologia (Curitiba) ◽

10.1590/s1984-46702011000100004 ◽

2011 ◽

Vol 28 (1) ◽

pp. 23-30 ◽

Cited By ~ 24

Author(s):

Pedro F Fruet ◽

Eduardo R Secchi ◽

Juliana C Di Tullio ◽

Paul G Kinas

Keyword(s):

Tursiops Truncatus ◽

Bottlenose Dolphins ◽

Southern Brazil ◽

Patos Lagoon ◽

Patos Lagoon Estuary

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Temporal Trends in Per- and Polyfluoroalkyl Substances in Bottlenose Dolphins (Tursiops truncatus) of Indian River Lagoon, Florida and Charleston, South Carolina

Environmental Science & Technology ◽

10.1021/acs.est.9b04585 ◽

2019 ◽

Vol 53 (24) ◽

pp. 14194-14203 ◽

Cited By ~ 3

Author(s):

Katie M. Lynch ◽

Patricia A. Fair ◽

Magali Houde ◽

Derek C. G. Muir ◽

Kurunthachalam Kannan ◽

...

Keyword(s):

South Carolina ◽

Tursiops Truncatus ◽

Bottlenose Dolphins ◽

Temporal Trends ◽

Indian River Lagoon ◽

Indian River ◽

Polyfluoroalkyl Substances

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Lobomycosis in Bottlenose Dolphins (Tursiops truncatus) from the Indian River Lagoon, Florida: Estimation of Prevalence, Temporal Trends, and Spatial Distribution

EcoHealth ◽

10.1007/s10393-008-0187-8 ◽

2008 ◽

Vol 5 (3) ◽

pp. 289-297 ◽

Cited By ~ 38

Author(s):

M. Elizabeth Murdoch ◽

John S. Reif ◽

Marilyn Mazzoil ◽

Stephen D. McCulloch ◽

Patricia A. Fair ◽

...

Keyword(s):

Spatial Distribution ◽

Tursiops Truncatus ◽

Bottlenose Dolphins ◽

Temporal Trends ◽

Indian River Lagoon ◽

Indian River

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Biopsy darting of common bottlenose dolphins (Tursiops truncatus) in southern Brazil: evaluating effectiveness, short-term responses and wound healing

Latin American Journal of Aquatic Mammals ◽

10.5597/lajam00221 ◽

2017 ◽

Vol 11 (1-2) ◽

pp. 121-132 ◽

Cited By ~ 4

Author(s):

Pedro Friedrich Fruet ◽

Luciano Dalla Rosa ◽

Rodrigo C. Genoves ◽

Victor H. Valiati ◽

Thales R.O. De Freitas ◽

...

Keyword(s):

Wound Healing ◽

Tursiops Truncatus ◽

Local Level ◽

Bottlenose Dolphins ◽

Previous Attempt ◽

Southern Brazil ◽

Short Term ◽

Patos Lagoon ◽

Multiple Biopsy ◽

Sampling Effectiveness

Cetacean biopsy sampling is a widely used technique with undisputable scientific value. Although it is generally considered as a harmless technique with no apparent long-lasting effects, studies have recommended examining behavioral responses to evaluate potential impacts on individuals, groups and sampled populations. In this study, we evaluated individual behavioral reactions and wound-healing in common bottlenose dolphins (Tursiops truncatus) during a biopsy sampling program carried out in southern Brazil from 2003 to 2012, and compared sampling effectiveness between dedicated and opportunistic sampling surveys. Two hundred and fiftytwo biopsy attempts were made, resulting in 118 hits (48% of attempts) and 134 samples (52% of attempts) collected successfully. Responses to biopsy sampling were low-level, of short-term duration, and elicited similar reactions on the dolphins, irrespective of shot distance, sex of individuals, dolphins’ group size and pre-behavioral state. Dolphins subjected to multiple biopsy attempts reacted in a similar manner as in previous attempt(s), with no evidence of increasing the intensity of the reaction. Wounds could be monitored in 18 animals and healed over 18 to 35 days. Generally, wounds appeared to be covered by epidermis in about three weeks with no observed signs of skin infection. Our results agree with previous studies suggesting that biopsy sampling does not cause significant disturbance to the behavior of dolphins. At a local level, this study demonstrates that biopsy sampling of bottlenose dolphins in the Patos Lagoon Estuary is more effective, less costly and less intrusive when conducted opportunistically, but that long-term sampling is required to achieve a relatively good sample size from photoidentified individuals in the population.

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Dynamics and Viability of a Small, Estuarine-Resident Population of Lahille’s Bottlenose Dolphins From Southern Brazil

Frontiers in Marine Science ◽

10.3389/fmars.2020.593474 ◽

2021 ◽

Vol 7 ◽

Author(s):

Pedro F. Fruet ◽

Luciana M. Möller ◽

Eduardo R. Secchi

Keyword(s):

Coastal Waters ◽

Bottlenose Dolphins ◽

Population Viability Analysis ◽

Disease Outbreaks ◽

High Survival ◽

Southern Brazil ◽

Patos Lagoon ◽

Dolphin Population ◽

Protection Area ◽

By Catch

Identifying threatened populations and quantifying their vulnerability is crucial for establishing priorities for conservation and providing robust information for decision-making. Lahille’s bottlenose dolphins have been long subjected to by-catch mortality in gillnet fisheries in coastal waters of southern Brazil, particularly in the Patos Lagoon estuary (PLE) and adjacent coastal waters, where dolphins from three populations (or Management Units) show overlapping home ranges. In this study we used a stage-classified matrix population model to conduct a demographic analysis of the PLE’s population with life-history data estimated through an 8 years mark-recapture study. A population viability analysis (PVA) was used to run a series of simulations where the risk was assessed under different by-catch scenarios, taking into account the effects of parameter uncertainty and stochasticity in the projections. In the absence of by-catch, we estimated that this dolphin population would growth at a rate of about 3% annually (95% CI: 1.2–5.8%). Under current by-catch rates, prognoses indicated high probabilities of viability over the next 60 years. These optimistic prognoses appear to be associated with the high survival of adult females. However, the eventual removal of very few mature females (one every year or two) would result in a prominent likelihood of decline from its current abundance at all pre-specified levels. The viability of the population would be substantially improved if the survival of juveniles/sub-adults could be increased. This may be achieved through the recently implemented dolphin protection area, which prohibits gillnet fisheries in the core area of this population. If the protection area reduces the entanglement rates of the most impacted life-stages (i.e., juvenile/sub-adult dolphins), there would be a substantial chance of the PLE’s dolphin population increasing above 20% of its current size, which is here proposed as conservation goal. If met, this goal has the potential to promote habitat quality, increase genetic diversity and connectivity with adjacent populations, enhancing the ability of bottlenose dolphins in southern Brazil to cope with environmental change and potential disease outbreaks.

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