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:2/3/2016)... PUNE, India , February 3, 2016 ... to the new market research report "Automated Fingerprint Identification ... (Tenprint Search, Latent Search), Application (Banking & Finance, Government, ... 2020", published by MarketsandMarkets, the market is expected to ... estimated CAGR of 21.0% between 2015 and 2020. The ...
(Date:2/2/2016)... 2016 This BCC Research report provides ... reviewing the recent advances in high throughput ‘omic ... field forward. Includes forecast through 2019. ... and opportunities that exist in the bioinformatic market. ... as well as IT and bioinformatics service providers. ...
(Date:2/2/2016)... , Feb. 2, 2016  Based on ... Frost & Sullivan recognizes US-based Intelligent Retinal Imaging ... & Sullivan Award for New Product Innovation. IRIS, ... North America , is poised ... rapidly growing diabetic retinopathy market. The IRIS technology ...
Breaking Biology News(10 mins):
(Date:2/8/2016)... ... February 08, 2016 , ... Thomas J. Todorow has ... Vice President for Corporate Services and the Chief Financial Officer at The Children’s ... Operations, Treasury, Managed Care Contracting, Supply Chain, and Investments. , Prior to joining ...
(Date:2/8/2016)... ... 2016 , ... Information Management Services ( IMS ) is pleased to announce ... new technical foundation and is so significant it was endowed with a new name, ... for search results, a streamlined layout and a more intuitive format for navigating the ...
(Date:2/8/2016)... ... February 08, 2016 , ... ... leading supplier of Semantic Graph Database technology, today announced the availability of AllegroGraph ... Cloudera Enterprise through the Cloudera Certified Technology Program (CCPT). AllegroGraph is ...
(Date:2/8/2016)... has an active R&D program for the development of ... Group has a unique research and development center in ... Bio Control products. Stockton has a ... regulatory guidelines, and is active in more than 35 counties ... Stockton,s flagship product Timorex Gold ® ...
Breaking Biology Technology: