Stock Illustration - smoking gun. fotosearch - search clipart, illustration, drawings and vector eps graphics images The Decline of River Herring: fact vs. fiction and is there a smoking gun? Mike Armstrong http://env-fp-nb-002/wiki/index .php?title=Image:MF_logo_white.png MF_logo_white alewife-fletcher River Herring – alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) alewife http://ipswichriver.org/wp-cont ent/uploads/2011/05/eone-river-herring-600-mfk1.jpg http://www.ens-newswire.com/ens /sep2010/20100920_herring.jpg Relevant Factoids for River Herring Anadromous Natal Homing ? Hundreds of genetic stocks Mature at 3 - 5 years old Spawning differences between the species Saltwater Freshwater Life Cycle of Anadromous Fishes Spawning Growth Spawning migration (Adults) Outward migration (Juveniles & adults) http://image24.webshots.com/25/2/66/96/37026696kFjner_ph.jpg http://www.nefsc.noaa.gov/sos/a rtwork/fig0075a.jpg Historical Significance River Herring Human Predation Deteriorating Water and Habitat Quality in Spawning/Juvenile Areas Passage Problems Water Withdrawals Increasing Predation By-catch in Pelagic Fisheries Historic River Herring Abundance in Massachusetts Colonial Dams Industrial Revolution DMF fishway projects 9 runs in Mass Bay (Belding 1920) 100 runs Ca. 200 runs First Fishway 1620 Generalized decline of river herring populations on the U.S. East Coast over the last decade Many possible causes: Overfishing Legal harvest Poaching By-catch in trawl fisheries Increased predation: striped bass, seals, commorants, dogfish, etc. Unknown environmental factors affecting recruitment alewife-fletcher In response, ASMFC sponsored a review of stock status Difficult to assess owing to population complexity Lack of data, particularly for southern runs In general –increasing total mortality (Z) and truncation of age structure Most runs showed some level of decline, very significant declines in some cases More than one pattern of decline Change in Length of Monument River Alewives Change in Length of Monument River Alewives Contemporary Age Structure of Alewives in Massachusetts Rivers Z > 1 Patterns of River Herring Spawning Run Counts Results of Cluster Analysis Run Counts 1983-2007 Rhode Island Runs Summary of Count Data for Southern New England Alewife Runs Synoptic declines beginning about 2002-2003 Runs reached lowest abundance in 2005-2006(+/-) So- What Happened? Alewife in danger –” the decline in the numbers of herring can be traced directly to the large trawlers that catch fish in critical spawning areas “ “Populations of river herring and shad are being decimated by commercial fishing along the Eastern seaboard, an environmental group claims in a lawsuit filed Monday against fisheries regulators.” “The group says fishermen trawling for mackerel and sea herring also are scooping up millions of river herring and shad” “But the fish have not rebounded to levels of even a decade ago. Conservation groups think they know why: Trawlers for sea herring are dragging the smaller river herring, which spawn in sea water, into their nets” Assorted Newspaper Quotes Monument River Count Midwater fleet begins River Herring Landings from US Waters Striped Bass declared recovered Pelagic fleet begins operation Change in Length of Monument River Alewives Midwater fleet begins River herring bycatch in Jan-Mar (per haul basis) River Herring By-Catch (Jan-Mar) By-Catch of River Herring in Sea Herring Fishery from port and sea sampling (MADMF, MEDMR, NMFS) 2008 & 2009 = about 700,000 lbs pairswd 2010 Maine Alewife Fishery 1.3 million lbs All fleets 530,00 lbs Directed Herring Fleet 166,000 lbs. What’s the population size of River Herring? 750 mill were taken in one year from the Potomac in the 1700’s Current coastwide population about 80 million adults (guesstimate) 1969- 200 mill lbs landed coast wide= 450 mill. Fish 1958- 34 mill lbs landed in MA = 85 mill fish……….about 5 mill today Predation About 25 million age 3+ striped bass If each individual ate 1 adult river herring, that’s about 15 times the sea herring fisheries by-catch/discard. Add cormorants, seals, dogfish, etc. R = 0.92 Blueback herring @ Holyhoke vs. Striped Bass Population (1983 – 2006) R = 0.92 By-Catch of River Herring in Sea Herring Fishery from port and sea sampling (MADMF, MEDMR, NMFS) 2008 & 2009 = about 700,000 lbs pairswd 2010 Maine Alewife Fishery 1.3 million lbs All fleets 530,00 lbs Directed Herring Fleet 166,000 lbs. What’s the population size of River Herring? 750 mill were taken in one year from the Potomac in the 1700’s Current coastwide population about 80 million adults (guesstimate) 1969- 200 mill lbs landed coast wide= 450 mill. Fish 1958- 34 mill lbs landed in MA = 85 mill fish……….about 5 mill today Predation About 25 million age 3+ striped bass If each individual ate 1 adult river herring, that’s about 15 times the sea herring fisheries by-catch/discard. Add cormorants, seals, dogfish, etc. R = 0.92 Blueback herring @ Holyhoke vs. Striped Bass Population (1983 – 2006) R = 0.92 Clearly we need to look beyond by-catch as the primary cause of the recent river herring decline Patterns in Spawning Run Demographics (What was going on in the runs during the decline?) sampling locations-river herring Age Sampling Locations Nemasket River Alewives Proportion at age (from age sampling) * run count = #’s at age Monument River Alewives Year Class Strength as indexed at Age-5 Monument River YC Strength Summary of Ageing Weak year classes seen across river systems YC 2000, 2001, 2002 (2003) were very weak Declines in runs were the result of weak year classes recruiting to the runs The weak year classes entered the run weak, i.e., the cause of the weakness runs The weak year classes entered the run weak, i.e., the cause of the weakness Possible Causes of Poor Year Classes Entering the Runs High mortality on pre-recruits (age-0,1, 2) Poor egg or larval survival Were the poor year classes created in the early life history or later when they were part of the coastal population? Alewife Juvenile Indices Monument River Alewives Alewife Juvenile Indices Monument River Alewives Relationship between Autumn rainfall and Spawner Abundance What’s the Mechanism for low rainfall in Autumn causing poor recruitment? Changes in zooplankton, water chemistry Delayed emigration – inc. predation and starvation No cues to induce emigration from ponds No or poor access for emigration Most ponds have dams Many streams become very low Conclusions from demographic study Weak year classes resulting from events occurring at the early life history stage caused the decline of alewife spawning populations in southern New England Weak year classes co-occurred at geographically separate rivers, indicating the causative factor was widespread – regional rainfall appears to be a pretty good candidate! We don’t need to invoke coastal predation or fishing mortality to explain this decline. Summary No single “smoking gun” All sources of mortality are increasing on an already “stressed population” contributing to the longer term decline. Short term decline appears related to poor recruitment Ecosystem management is likely needed