Navigation Links
Dolphin population stunted by fishing activities, Scripps/NOAA study finds
Date:11/24/2008

Despite broad "dolphin safe" practices, fishing activities have continued to restrict the growth of at least one Pacific Ocean dolphin population, a new report led by a researcher at Scripps Institution of Oceanography at UC San Diego has concluded.

Populations of dolphins in the Eastern Pacific were expected to increase in abundance after successful regulations and agreements were enacted to reduce dolphin deaths as a result of fishing "bycatch," cases in which animals are caught unintentionally along with intended targets.

But the new study, published in the October issue of Marine Ecology Progress Series, reveals that negative impacts from fishing activities remain. Instead of reducing numbers through direct mortalities, the study by Katie Cramer of Scripps Institution of Oceanography and Wayne Perryman and Tim Gerrodette of the National Oceanic and Atmospheric Administration's (NOAA's) Southwest Fisheries Science Center shows that fishing activities have disrupted the reproductive output of the northeastern pantropical spotted dolphin. The researchers note that reproductive output of the eastern spinner dolphin also declined, but a direct link to fishing effort was inconclusive.

"The results of this study clearly show that depleted dolphin populations have failed to recover in part due to a decline in reproductive output, and that fishing has had an effect on reproduction," said Cramer, a graduate student researcher in the Scripps Center for Marine Biodiversity and Conservation. "This shows that the fisheries indeed are still having an impact."

The new conclusions are based on broad surveys conducted by NOAA Fisheries Service between 1987 and 2003 designed to assess the size and health of dolphin populations in the eastern Pacific Ocean. The surveys included military reconnaissance camera images of more than 20,000 animals.

Cramer, who participated in helicopter surveys between 1998 and 2003, and her colleagues used the image database to analyze entire dolphin schools, focusing in particular on mother-calf pairs.

The scientists compared the data with the number of fishing events in which a dolphin school is chased by speedboats and encircled in a large "purse-seine" net in order to capture the large yellowfin tuna that often swim with dolphin schools. While such fishing led to high dolphin mortalities after purse-seine fishing was launched in the eastern tropical Pacific in the 1950s, bycatch deaths declined by the end of the 1990s due to new fishing techniques that ensured that dolphins are eventually released from the nets alive.

Yet despite mortality reductions, dolphin populations have not recovered at a rate expected since bycatch was reduced.

Using the aerial photographic database, Cramer and her colleagues found a strong link between the amount of fishing and reproductive output in a given year for the dolphin population most heavily targeted by the fishery, the northeastern pantropical spotted dolphin. Both the proportion of adult animals in the photographs with a calf, and the length at which calves disassociated from their mothers (a measure of the length at which the calves stop nursing), declined with increasing fishing effort.

Together, the results showed that fishing had a negative impact on calf survival rates and/or birth rates. This could be caused when fishing operations separate mothers from their suckling calves, interfere with the conception or gestation of calves or a combination of the two.

"The link between fishing activity and reproductive output indicates that the fishery has population-level effects beyond reported direct kill," the authors write in their report.

What remains unknown is the exact mechanism leading to reduced reproductive output. This question is currently being investigated by researchers at NOAA Fisheries' Southwest Fisheries Science Center in La Jolla.


'/>"/>

Contact: Mario Aguilera or Annie Reisewitz
scrippsnews@ucsd.edu
858-534-3624
University of California - San Diego
Source:Eurekalert  

Related biology news :

1. Baiji Dolphin previously thought extinct spotted in the Yangtze River
2. Migrating squid drove evolution of sonar in whales and dolphins, researchers argue
3. Scientists fear rare dolphin driven to extinction by human activities
4. Dolphin therapy a dangerous fad, Emory researchers warn
5. NOAA study shows eastern tropical pacific ocean dolphin populations improving
6. Mercury contamination found in stranded Victorian dolphins
7. Killer whales, blind bats, discriminating dolphins, mating birds
8. Study shows rise in Cornwalls dolphin, whale and porpoise deaths
9. Whales and dolphins influence new wind turbine design
10. Study sheds new light on dolphin coordination during predation
11. Population movements and money remittances spur forest regrowth
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Dolphin population stunted by fishing activities, Scripps/NOAA study finds
(Date:12/6/2016)... -- Securus Technologies, a leading provider of civil ... investigation, corrections and monitoring, and the Prison Entrepreneurship ... year funding commitment by Securus to PEP and ... reentry support to more inmates and their families. ... Prison Entrepreneurship Program (PEP) is an independent 501(c)(3) ...
(Date:12/2/2016)... 2016   SoftServe , a global digital ... an electrocardiogram (ECG) biosensor analysis system for continuous ... asset. The smart system ensures device-to-device communication between ... and mobile devices to easily ,recognize, and monitor ... vehicle technology advances, so too must the security ...
(Date:11/29/2016)... BOSTON , Nov. 29, 2016 BioDirection, ... rapid point-of-care products for the objective detection of concussion ... the company has successfully completed a meeting with the ... company,s Tbit™ blood test Pre-Submission Package. During the meeting ... Tbit™ system as a precursor to commencement of a ...
Breaking Biology News(10 mins):
(Date:12/7/2016)... Regen BioPharma Inc. (OTCQB: RGBPP) In ... Sciences a team of scientists in Guangzhou, China ... that expression of NR2F6 in patients with early cervical cancer ... patient,s cervical cancer tissue as well as in the normal ... an interesting study and the first that I am aware ...
(Date:12/7/2016)... Woods Hole, Massachusetts (PRWEB) , ... December 07, 2016 , ... Kara Dwyer Dodge grew ... 1966, Richard Dwyer, a third-generation fisherman in Scituate, Mass., found a sea turtle entangled in ... to shore, where the turtle became a minor sensation because no one could remember ever ...
(Date:12/6/2016)... ... December 06, 2016 , ... Discovering new clues to natural treatments that ... what’s happening in our brains. And searching for keys to our immune systems by ... honored with the 2017 Edith and Peter O’Donnell Awards by The ...
(Date:12/6/2016)... SAN DIEGO , Dec. 6, 2016 ... of Santosh Kesari , MD, PhD, FANA, FAAN ... his experience in neurology and clinical trials to assist ... for treatment of stroke. The AmnioStem product is a universal ... previously shown therapeutic activity in animal models of stroke ...
Breaking Biology Technology: