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:1/28/2016)... JOSE, Calif., Jan. 28, 2016 Synaptics (NASDAQ: SYNA ... results for its second quarter ended December 31, 2015. ... second quarter of fiscal 2016 increased 2 percent compared to the ... second quarter of fiscal 2016 was $35.0 million, or $0.93 per ... Non-GAAP net income for the first quarter of fiscal 2016 grew ...
(Date:1/22/2016)... January 22, 2016 ... addition of the  "Global Behavioral Biometric ... --> http://www.researchandmarkets.com/research/4lmf2s/global_behavioral ) has ... Behavioral Biometric Market 2016-2020"  report to ... and Markets ( http://www.researchandmarkets.com/research/4lmf2s/global_behavioral ) has announced ...
(Date:1/20/2016)... Minn. , Jan. 20, 2016   MedNet ... supports the entire spectrum of clinical research, is pleased ... 2015. MedNet,s significant achievements are the result of the ... iMedNet eClinical , it,s comprehensive, easy-to-use ... --> --> Key MedNet growth achievements ...
Breaking Biology News(10 mins):
(Date:2/4/2016)... San Francisco, CA (PRWEB) , ... February 04, ... ... future of enterprise talent development and compliance training, today announced an interactive ... on Morf Playbook™. The RAPS (Regulatory Affairs Professional Society) accredited interactive course ...
(Date:2/4/2016)... ... February 04, 2016 , ... ... by Bloomsburg University’s Digital Forensics Club, takes place February 5-6 at the ... features 20+ speakers and activities such as workshops and competitions for ample ...
(Date:2/4/2016)... --> --> Q BioMed ... provide the following update on recent corporate developments. ... months we have significantly increased our cash position through several ... result, we have positioned ourselves to execute on the initial ... that development to continue on schedule. --> ...
(Date:2/4/2016)... ... February 04, 2016 , ... Franz Inc. ... Graph Database technology has been recognized As “ Best in Semantic Web Technology ... , “At Corporate America, it’s our priority to showcase prominent professionals who are ...
Breaking Biology Technology: