Seasons' End ~ Fishing

24 – SEASONS’ END: Global Warming’s Threat to Hunting and Fishing

Freshwater Fish

A

little rise in water temperature here, a small drop in water

level there, a few more days of drought . . . does it really add up to DOO WKDW PXFK" )RU WURXW ZDOOH\H EDVV SLNH DQG RWKHU IUHVKZDWHU ÀVKHV LW DGGV XS to a lot. In fact, put it all together and you have a crisis that could take the magic out of those graphite wands.

While predictions of global warming are serious for all freshwater Ă€VK WKH\ DUH GLUH IRU WURXW ´,W GRHVQ¡W WDNH D ELJ MXPS LQ WKH WHPSHUature of a stream to wipe out a population of brookies,â€? says Steve Moyer, Trout Unlimited’s vice president for governmental affairs. “And it happens so fast — seems like they disappear while you’re VZLWFKLQJ \RXU Ă \ IURP D Q\PSK WR D GU\ Âľ

FRESHWATER FISH – 25

As snowpack decreases in volume and melts earlier in the season and

Current projections of the effect of global warming on freshwater

DV WHPSHUDWXUHV VKRRW XS LQ PLGVXPPHU VWUHDP Ă RZV ZLOO SOXP-

Ă€VK LQFOXGH WKH IROORZLQJ

met. “Trout in streams and rivers at upper elevations will be under a

•

Nationally, up to 42 percent of current trout and salmon habitat

great deal of stress,� says Dr. Jack Williams, Trout Unlimited’s senior

will be lost before the end of the century, with the South, South-

scientist. “At lower elevations they’re just not going to survive with-

west and Northeast experiencing especially severe reductions.

out a lot of help.�

•

In regions most affected by global warming, trout and salmon populations will be slashed by 50 percent or more. Many trout

While more able than trout to adapt to increased water temperatures,

species already listed as threatened or endangered will become

bass, bluegill and other warm-water species will face other threats from global warming. For example, changes in precipitation pat-

increasingly vulnerable to extinction. ‡ ,Q WKH 3DFLÀF 1RUWKZHVW XS WR SHUFHQW RI WKH VDOPRQ SRSXOD-

WHUQV Âł KHDY\ Ă RRG SURGXFLQJ UDLQV LQWHUVSHUVHG ZLWK H[WHQGHG GURXJKWV Âł ZLOO FDXVH PDMRU Ă XFWXDWLRQV LQ ZDWHU OHYHOV ,Q ODNHV

tion will disappear. •

ULYHUV DQG UHVHUYRLUV WKHVH Ă XFWXDWLRQV FRXOG GUDPDWLFDOO\ UHGXFH

In localized, high-mountain areas of the West, bull trout will suffer reductions of up to 90 percent. In the lower elevations of the

the survival rate of eggs, larvae and fry. “Occasional extreme events

Appalachian Mountains, as much as 97 percent of the wild trout

have always been part of the weather cycle, but with global warm-

population will die.

LQJ WKHVH H[FHSWLRQV FRXOG EHFRPH WKH UXOH ¾ VD\V -RKQ /RWW ÀVKHULHV

•

Sea-level rise will push salt water into rivers, over low-lying

chief at the South Dakota Department of Game, Fish and Parks. “If

land and into freshwater lakes. This salinity will contract suit-

VR UHFUXLWPHQW LQWR DGXOW ÀVK DPRQJ DOO IUHVKZDWHU VSHFLHV ZRXOG EH

DEOH KDELWDW IRU ZDUP ZDWHU ÀVKHV WKDW UHTXLUH ZDWHU ZLWK ORZ

seriously jeopardized.�

or no salinity.

26 – SEASONS’ END: Global Warming’s Threat to Hunting and Fishing

•

Across the nation, increased water temperatures in rivers and lakes will promote the continued expansion of noxious, exotic plant species such as giant salvinia, hydrilla and Eurasian watermilfoil.

‡ %HFDXVH ÀVK UHFUXLWPHQW LQ ULYHUV DQG ODNHV LV IUHTXHQWO\ WLHG WR ZDWHU OHYHOV H[WUHPH GURXJKWV DQG à RRGV ZLOO FDXVH ODUJH à XFWXDWLRQV LQ WKH TXDOLW\ RI UHFUHDWLRQDO ÀVKHULHV

What Global Warming Means on the Water Although predicting the exact timing and effects of global warming RQ ÀVKHULHV LV DW EHVW GLIÀFXOW DQJOHUV VKRXOG EH SUHSDUHG WR VHH VLJQLÀFDQW FKDQJHV WR WKHLU VSRUW RYHU WLPH

Familiar fishing holes just won’t stay the same As higher temperatures accelerate evaporation and contribute to GURXJKW ZDWHU OHYHOV ZLOO IDOO LQ PDQ\ IDYRULWH ÀVKLQJ ORFDOHV — small ponds, water-supply reservoirs, local creeks and streams, and SXEOLF DQG SULYDWH GDPV 7KLV ZLOO VWUHVV ÀVK SRSXODWLRQV DQG DIIHFW

FRESHWATER FISH – 27

angler access. Places popular for family recreation may cease to be SODFHV ZKHUH NLGV FDQ OHDUQ WR ÀVK

Favorite fish will relocate $V ÀVK UHVSRQG WR JOREDO ZDUPLQJ E\ PRYLQJ WR QHZ ORFDWLRQV anglers may have to travel farther to catch their favorite species. Or they might be forced to adapt by changing their target species from FRRO DQG FROG ZDWHU ÀVKHV VXFK DV ZDOOH\H WURXW RU VDOPRQ WR RWKHU PRUH UHVLOLHQW VSHFLHV WKDW FDQ à RXULVK XQGHU ZDUPLQJ FRQGLWLRQV

Anglers’ support will be critical to preserve public water rights Policies that protect recreational use of increasingly scarce water reVRXUFHV DQG UHGXFH VWUHVV RQ ÀVK ZLOO OLNHO\ FRQà LFW ZLWK HIIRUWV WR expand control over these same resources for private gain. Anglers’ ZLOOLQJQHVV WR ÀJKW IRU ZDWHU TXDOLW\ ZDWHU OHYHOV DQG ZDWHU à RZV in their favorite lakes, streams and reservoirs will be essential to the success of management plans that safeguard public-trust rights to water.

28 – SEASONS’ END: Global Warming’s Threat to Hunting and Fishing

Changing conditions will shape management practices and regulations

actions management agencies undertake in response to changing

$FWLRQV WR VWDELOL]H ÀVKHULHV LQ OLJKW RI WKH FRQVHTXHQFHV RI JOREDO

WKH LQFUHDVLQJO\ LPSRUWDQW SDUWQHUVKLS EHWZHHQ WKH ÀVKLQJ FRPPX-

warming may include

nity and management agencies.

conditions. Understanding management decisions will strengthen

‡ XVLQJ KDUYHVW UHJXODWLRQV WR SURWHFW DGXOW ÀVK •

promoting water use and water allocation measures to protect

Protecting fish and habitat will increase the odds of fishes’ adapting

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are great, much can be done to build resistance to global warming’s HIIHFWV 3URWHFWLQJ KLJK TXDOLW\ KDELWDWV DQG FXUUHQWO\ KHDOWK\ ÀVK

Anglers must educate themselves about adaptive management and

SRSXODWLRQV ZLOO VFLHQWLVWV EHOLHYH IRVWHU ÀVKHV¡ SRWHQWLDO WR DGDSW WR

KRZ LW LQĂ XHQFHV UHJXODWLRQV 7KH\ ZLOO QHHG WR VWD\ LQIRUPHG DERXW

warming water temperatures and other habitat changes.

FRESHWATER FISH – 29

30 – SEASONS’ END: Global Warming’s Threat to Hunting and Fishing

F

FRROHU ZDWHU PLJKW EH DEOH WR ÀQG LW DW KLJKHU HOHYDWLRQV DW PRUH UHVKZDWHU ÀVKHV ZLOO H[SHULHQFH WKH HIIHFWV RI JOREDO FOLPDWH

change primarily through warming water temperatures and changes LQ UDLQIDOO DQG VWUHDP Ă RZ &OLPDWH FKDQJH ZLOO EHQHĂ€W VRPH VSH-

northerly latitudes or in deeper lakes. However, if passage to more VXLWDEOH FRQGLWLRQV LV EORFNHG ÀVK SRSXODWLRQV PD\ EHFRPH IUDJmented, decline and face local extinctions.

cies as their range expands or as prey increases; other species will

A nationwide analysis of the effects of warmer air temperature esti-

decline as their habitats contract and they are physiologically un-

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DEOH WR DGDSW WR ZDUPHU FRQGLWLRQV *UHDWHU YROXPHV RI VWUHDP Ă RZ

itat could be lost by 2030, rising to 21 percent to 42 percent by 2090.

FRXOG GHOLYHU PRUH QXWULHQWV WR ÀVK RU UDLVH PRUWDOLW\ E\ LQFUHDVLQJ

Although substantial losses are expected throughout all regions of

scouring and turbidity. Changes in species’ presence and abundance

North America, losses in the South, Southwest and Northeast could

ZLOO RIWHQ UHIDVKLRQ IUHVKZDWHU ÀVK FRPPXQLWLHV WR WKH GHWULPHQW RI

EH SDUWLFXODUO\ VHYHUH 0RVW YXOQHUDEOH DUH ÀVK SRSXODWLRQV DW WKH

native species.

limits of their ranges, such as salmon in California and bull trout in the high-mountain areas of the West. Modeling an increase of 5.4 degrees Fahrenheit in July air temperature predicts losses of

Global Warming and Freshwater Fish Habitat The water in rivers, streams, lakes and ponds, in puddles, brooks DQG ÀVKLQJ KROHV LV VHQVLWLYH ERWK WR LQFUHDVHG DLU WHPSHUDWXUHV DQG

stream habitat ranging up to 24 percent for Bonneville cutthroat trout and 38 percent for westslope cutthroat trout. Scientists estimate that up to 90 percent of the wild brook trout in the Appalachians could be lost due to climate change.

to altered weather patterns. Alterations in these two factors will

Already the effect of rising temperatures has been documented in lo-

FDXVH IDU UHDFKLQJ FKDQJHV LQ ÀVK KDELWDWV DQG E\ H[WHQVLRQ LQ ÀVK

cations throughout the country. If stream temperatures in Maryland

populations.

rise a few additional degrees, the eastern brook trout in the western part of the state and even the brown trout will lose the cold-water

Temperature and fish habitat

habitat necessary for survival. In Rapid Creek — a favorite desti-

As air temperatures rise, water warms. Fish thrive within a tempera-

nation among South Dakota anglers — brown trout numbers have

ture range that varies from species to species; temperatures exceed-

fallen by more than 90 percent, due primarily to prolonged drought

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DQG DVVRFLDWHG ORZ VWUHDP Ă RZ ,Q 0LQQHVRWD LW LV TXLWH SUREDEOH

FRESHWATER FISH – 31

that lake trout will not persist in lakes currently unable to provide an

could decrease water transparency, stunting growth of submersed

oxygen-rich environment in their deepest, coldest portions.

plants. And invasive plant species, with their fast growth rates and

Lake trout are highly sensitive to increased temperatures. Though in certain cases lake habitats may provide important refuge, most lakes in the lower 48 United States are predicted to become less hosSLWDEOH WR FROG ZDWHU ÀVKHV *OREDO ZDUPLQJ LV OLNHO\ WR SURGXFH HDUO\ VHDVRQ VWUDWLÀFDWLRQ ³ WKH SKHQRPHQRQ RI ZDUP EXR\DQW lake water lying atop cooler, denser water. Preventing wind-driven mixing of the thermal layers and delivery of oxygen to the lower GHSWKV VWUDWLÀFDWLRQ FDXVHV WR[LF DOJDH EORRPV LQFUHDVHV WKH UHOHDVH of contaminants from bottom sediments and exacerbates summer ÀVK NLOO 'HVSLWH GHFUHDVHG ZLQWHU PRUWDOLW\ ÀVK ORVVHV DUH H[SHFWed to increase overall due to summerkills in all but the deepest and coldest northern lakes.

ODFN RI QDWXUDO FRPSHWLWRUV DUH H[SHFWHG WR EHQHÀW PRVW IURP JOREDO ZDUPLQJ WKHLU HIIHFWV RQ ÀVK ZRXOG YDU\ DQG ZRXOG QRW EH FRQVLVWHQWO\ EHQHÀFLDO 6KRUHOLQH YHJHWDWLRQ FRQWULEXWHV WR TXDOLW\ ÀVK KDELWDW E\ PRGHUDWing runoff and providing cooling shade. Management practices that PDLQWDLQ ULSDULDQ à RUD FRXOG PLWLJDWH WKH à RRGV DQG KLJK WHPSHUDtures expected to occur under global warming.

Sea-level rise and habitat Sea-level rise, another consequence of global warming, will push saline water farther into rivers, low-lying lands and freshwater aquifers. As a result, habitat of saltwater-intolerant species will contract.

9HJHWDWLRQ SOD\V D QXPEHU RI FULWLFDO UROHV LQ IUHVKZDWHU ÀVK KDELWDW

Organisms in coastal areas offering no escape from high-salinity

providing refuge; supplying nutrition to the food web; stabilizing

conditions — such as low-elevation wetlands and dammed coastal

DTXDWLF DUHDV PRGHUDWLQJ ZDWHU Ă RZ DQG WHPSHUDWXUH DQG LQĂ XHQF-

rivers — will be most vulnerable to the effects of saltwater

ing water quality by affecting sedimentation, contributing dissolved

intrusion.

oxygen, and cycling nutrients and other chemicals.

Rising temperatures may remove limitations imposed by frost kill,

Precipitation and habitat

winter dormancy and abbreviated growing seasons on the range and

Like rising temperatures, changes in weather patterns due to global

JURZWK RI PDQ\ DTXDWLF SODQWV )LVK FRXOG EHQHĂ€W IURP WKH UHVXOWLQJ

warming could severely affect aquatic habitats. Extreme variations

increase in plant diversity and expansion of vegetative cover. How-

LQ UDLQ DQG VQRZIDOO LQ GHOXJHV DQG GURXJKWV ZRXOG GLVUXSW ÀVK

ever, warmer temperatures accelerate phytoplankton growth, which

and invertebrate community structures in a number of ways.

32 – SEASONS’ END: Global Warming’s Threat to Hunting and Fishing

FRESHWATER FISH – 33

'HOXJHV à XVK QXWULHQWV DFLGV VLOW DQG SROOXWDQWV LQWR ODNHV VWUHDPV DQG ULYHUV UHVXOWLQJ LQ WKH GLUHFW PRUWDOLW\ RI ÀVK LQ DOO OLIH stages. High levels of dissolved and suspended particles degrade all IUHVKZDWHU ÀVK KDELWDW ODQGVOLGHV UHVXOWLQJ IURP GHOXJHV FDQ FDXVH catastrophic loss in local populations. Because they cannot survive ZLWKRXW FROG KLJKO\ R[\JHQDWHG à RZLQJ ZDWHU WURXW ZLOO EH DPRQJ those most affected by the rapid runoff following extreme storms and heavy rains.

Floods damage aquatic vegetation, especially during winter, by destabilizing the shoreline, uprooting established plants and disUXSWLQJ URRWLQJ ]RQHV DQG VHHGEHGV 6HGLPHQW ODGHQ Ă RRGZDWHUV restrict the growth of submersed plants by limiting depths at which light is available.

2WKHU HIIHFWV RI JOREDO ZDUPLQJ FRXOG EHQHÀW DTXDWLF SODQWV KRZever. As warmer temperatures cause ice covers on northern lakes to thin and be of shorter duration, plants could receive more light, experience a longer growing season, and colonize and overwinter more successfully. %XW RYHUDOO FKDQJHV LQ LFH FRYHU PD\ SURYH GHWULPHQWDO WR ÀVK habitat. Lake Superior has already warmed twice as much as air temperatures, which may be due to a lack of ice cover. As a result, Lake Superior’s water levels are the lowest in recorded history.

34 – SEASONS’ END: Global Warming’s Threat to Hunting and Fishing

Drought

7HPSHUDWXUHV H[FHHGLQJ WKRVH WR ZKLFK D ÀVK LV DGDSWHG FDQ EH

The variable weather patterns predicted to accompany global warm-

taxing. Low dissolved oxygen, commonly associated with warmer

LQJ ZLOO FDXVH UHJLRQDO GURXJKWV DV ZHOO DV Ă RRGV ,Q VRPH SODFHV

temperatures, is an additional stress. These two factors are powerful

persistent drought, combined with high water temperatures, has al-

determinants of what species inhabit an area.

UHDG\ GLPLQLVKHG ZDWHU UHVHUYRLUV VR VHYHUHO\ DV WR HQGDQJHU ÀVK For example, in Georgia’s Lake Lanier, prolonged drought has forced

Warmer temperatures would improve conditions in high elevations

EDLW ÀVK WR FRQFHQWUDWH LQ UHFHGLQJ ZDWHUV D VKRUW WHUP ERRQ WR WKH

DQG QRUWKHUQ ODWLWXGHV KLVWRULFDOO\ WRR FROG WR VXVWDLQ ÀVK SRSXOD-

ODNH¡V EDVV EXW D ORQJ WHUP WKUHDW WR WKH ÀVKHU\¡V VWDELOLW\

tions. However, species that dwell in lower elevations or more southerly latitudes could suffer increased temperature-related mortality.

Long periods of drought will cause regional declines in the abundance of aquatic plants and lead to changes in the composition of vegetative communities.

6WDUYDWLRQ FRXOG DOVR UHVXOW IURP KHDW DV ÀVK H[SHQG PRUH HQHUJ\ on maintaining metabolic functions and less energy on feeding and growth.

$OWKRXJK QDWLYH ÀVKHV DUH ZHOO DGDSWHG WR QDWXUDO ÀUH UHJLPHV WKH LQFUHDVHG IUHTXHQF\ DQG LQWHQVLW\ RI ZLOGÀUHV FDXVHG E\ JOREDO warming will be detrimental because of loss of riparian vegetation and increased sediment delivery.

Many lower-latitude trout habitats may already sustain temperatures that cause summerkills and starvation. Rainbows usually die when waters reach about 70 degrees Fahrenheit over an extended time. Brown trout are able to survive slightly warmer waters, but not

Global Warming and Fish Health Temperature and fish physiology

for more than a couple of weeks. Global warming would push both of these species up to cooler places — to higher elevations or more northerly streams.

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By producing unhealthy conditions, global warming will increase

linked to water temperature. Typically, metabolism operates best

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QHDU WKH XSSHU OLPLW RI D ÀVK¡V WKHUPDO QLFKH :KHQ LGHDO PHWDEROLF

causing whirling disease, proliferative kidney disease and other

IXQFWLRQ LV DFKLHYHG JURZWK ÀWQHVV DQG UHSURGXFWLYH FDSDELOLW\ DUH

maladies are expected to expand in distribution and increase in

maximized. Fish thrive.

virulence.

FRESHWATER FISH – 35

36 – SEASONS’ END: Global Warming’s Threat to Hunting and Fishing

7R[LQV Ă XVKHG LQWR DTXDWLF V\VWHPV E\ UDLQVWRUPV DQG Ă RRGV SRVH

Missouri River water to be released for authorized purposes down-

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VWUHDP ZLOO FRQWLQXH WR VWUHVV WKHVH SRSXODWLRQV RI EDLWĂ€VK

follow extreme high-water events and concentrate the toxins in diminished volumes of water.

Other Midwestern states face similar problems. In Minnesota there are currently about 650 lakes with the conditions of temperature and

Global Warming and the Food Web Warming temperatures can boost the productivity of an aquatic sysWHP DQG UHRUGHU WKH LQWULFDWH ÀVK IRRG ZHE :KLOH IRRG VRXUFHV IRU

water quality needed to maintain a population of ciscoes. AccordLQJ WR ÀVKHULHV PDQDJHUV ZLWKLQ \HDUV RQO\ WR ODNHV ZLOO remain healthy enough to support ciscoes.

VRPH VWDJHV RI ÀVK GHYHORSPHQW FRXOG EHFRPH PRUH SOHQWLIXO ZDUP

)LVK WKDW IHHG RQ LQVHFWV ZLOO DOVR ÀQG DGMXVWPHQW GLIÀFXOW )RU H[DP-

temperatures could reduce availability of prey dependent on cold

SOH ZLWK UHGXFHG VQRZSDFN DQG HDUOLHU UXQRII PD\Ă LHV DQG RWKHU

water.

aquatic insects are likely to emerge earlier. Though the results for

For instance, in the upper three Missouri River reservoirs in Montana and the Dakotas, healthy populations of species like walleye, northern pike, smallmouth bass and land-locked Chinook salmon exist because cold-water habitat is available. These species experience optimal growth at temperatures found in the cold-water OD\HU QHDU WKH ERWWRP RI WKH UHVHUYRLUV GXULQJ VXPPHU VWUDWLĂ€FDWLRQ

Ă€VK DQG WKH EURDGHU DTXDWLF FRPPXQLW\ DUH XQFHUWDLQ WKH\ DUH PRVW likely to be detrimental. %LRORJLVWV SRVLW WKDW FRQVLVWHQWO\ ORZ VWUHDP Ă RZV FRQWULEXWH WR WKH explosive growth of didymo, an invasive algae that covers stream beds and destroys the plant and insect growth necessary for healthy brown trout. If so, global warming could worsen the problem.

Food for these predators — rainbow smelt and ciscoes — also inhabits this cold-water layer. As extended drought has caused decreased

The expected increase in erosion and sedimentation from storms,

ZDWHU OHYHOV DQG RYHUDOO ZDUPLQJ WHPSHUDWXUHV ÀVKHULHV PDQDJHUV

à RRGV DQG ZLOGÀUH ZLOO DIIHFW HYHU\ WLHU RI WKH ÀVK IRRG ZHE /RVV RI

have become increasingly concerned about the disappearance of cold-

riparian vegetation and warmer stream temperatures would cause

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declines among invertebrates, a chief source of nutrition for many

Global warming and continued drought, coupled with demands for

VWDJHV RI ÀVK OLIH

FRESHWATER FISH – 37

Global Warming and Life Histories Temperature and migrations

tion and reproductive age. Although many factors contribute, proper WHPSHUDWXUH LQLWLDWHV D ÀVK¡V VXFFHVVIXO UHSURGXFWLYH F\FOH

7KH OLIH KLVWRULHV RI IUHVKZDWHU JDPH ÀVK LQFOXGH PLJUDWLRQ PDWXUD-

An earlier onset of spring will advance the date at which waters are

tion, reproduction and recruitment. Predicted climate changes will,

suitably warm for spawning. In general, spawning temperatures for

WR D JUHDWHU RU OHVVHU GHJUHH LQĂ XHQFH DOO RI WKHVH SKDVHV :DUP-

ZDUP ZDWHU ÀVK UDQJH IURP PLQLPXPV RI WR GHJUHHV )DKU-

ing waters will likely have particularly dramatic impacts on the life

enheit to maximums of 60.8 to 84.2 degrees Fahrenheit — tempera-

F\FOHV RI FROG ZDWHU ÀVK LQFOXGLQJ WURXW FKDU DQG VDOPRQ

ture limits that will likely be exceeded in many regions as a result of

For instance, for most species migration and smolting — the move-

global warming.

ment of young salmonids from fresh water to the sea — coincide

In both rainbow and brook trout, an increase in temperature has been

with narrow temperature ranges. As increased temperatures and

shown to increase egg production. Faster egg development results

WKH DEEUHYLDWHG VSULQJ IUHVKHWV WKDW WKH\ FDXVH LQVWLJDWH VPROWLĂ€FD-

in better survival and, therefore, an increase in trout population.

tion earlier in the season, the proportion of smolts mature enough

However, other effects of global warming such as intense storms and

to migrate may shrink. In some species migratory behavior may be

LQFUHDVHG VWUHDP Ă RZ WKDW OHDG WR VFRXULQJ DQG UHGG PRUWDOLW\ FRXOG

lost altogether. In steelhead, for instance, smolts’ migration occurs

offset this advantage.

only when spring water temperatures are below 54 degrees Fahrenheit. Earlier out-migrations for all species may cause a mismatch

Rising temperatures will reduce ice cover and snowpack, affecting

between feeding needs and food-producing conditions in estuaries

life cycles of species dependent on these sources of cold. For exam-

and oceans.

SOH ODFN RI LFH FRYHU LQ /DNH 6XSHULRU MHRSDUGL]HV ZKLWHĂ€VK ZKLFK reproduce in shallow bays and rely on ice cover to protect their eggs

Temperature and reproduction

from storm disturbance. In warming waters temperature-sensitive

%RWK WHPSHUDWXUH DQG ZHDWKHU LQà XHQFH ÀVK UHSURGXFWLRQ DQG UH-

lake trout will require more food. It is likely that many lakes will be

cruitment. Warmer temperatures increase the growth rate of many

unable to supply enough summer nutrition to sustain healthy lake

ZDUP ZDWHU VSRUW ÀVK DQG GHFUHDVH WKH OHQJWK RI WLPH WR PDWXUD-

trout and fuel fall spawning.

38 – SEASONS’ END: Global Warming’s Threat to Hunting and Fishing

Precipitation, stream flow, sea-level rise and reproduction Made more variable by warming temperatures, changing precipitaWLRQ SDWWHUQV ZLOO DIIHFW ULYHU à RZ ODNH VWDJHV DQG RWKHU DVSHFWV RI DTXDWLF KDELWDW ZLWK ERWK EHQHÀFLDO DQG GHWULPHQWDO HIIHFWV RQ ÀVK reproduction and recruitment.

As an example, when scientists simulated a combination of altered à RZ DQG LQFUHDVHG WHPSHUDWXUH WKH\ IRXQG WKDW WKH JURZWK UDWHV RI XSVWUHDP UDLQERZ WURXW LQFUHDVHG VR PXFK WKDW WKH ÀVK PDWXUHG D year early. As a result, species abundance increased dramatically. In contrast, the fall-spawning brown trout suffered high incidences of UHGG VFRXULQJ IURP LQFUHDVHG ZLQWHU à RZV DQG JUHDWHU HJJ PRUWDOLW\ IURP GHZDWHULQJ ZKHQ UHGGV EXLOW DW KLJK à RZV EHFDPH H[SRVHG DV à RZV GHFUHDVHG $OWKRXJK DOO ÀVK ZRXOG VXIIHU XQGHU FRQGLWLRQV RI IUHTXHQW DQG SURORQJHG GURXJKW WKH TXDOLW\ RI UHFUHDWLRQDO ÀVKLQJ IRU FRRO ZDWHU ÀVK VXFK DV FKDQQHO FDWÀVK ZDOOH\H WLJHU PXVNLH DQG VWULSHG EDVV DV ZHOO DV VRPH ZDUP ZDWHU ÀVK OLNH VXQÀVK EODFN EDVV DQG FUDSSLH ZRXOG à XFWXDWH ZLWK YDULDEOH ZDWHU OHYHOV 8VLQJ KDUYHVW UHJXODWLRQV WR SURWHFW DGXOW ÀVK DQG ÀVK KDELWDW DQG DOORFDWLQJ ZDWHU UHVRXUFHV WR VWDELOL]H ÀVKHULHV DUH DPRQJ WKH PDQDJHPHQW SUDFWLFHV WKDW FDQ PLWLJDWH WKH HIIHFWV RI JOREDO ZDUPLQJ RQ IUHVKZDWHU ÀVK

FRESHWATER FISH – 39

Global Warming and Population Distribution As global warming alters ecosystems across the country, some species’ ranges will expand while others will contract. Most reductions LQ WKH UDQJHV RI IUHVKZDWHU ÀVK ZLOO RFFXU IURP VRXWK WR QRUWK DQG VRPHZKDW OHVV IURP HDVW WR ZHVW /RVW IUHVKZDWHU ÀVK KDELWDW FRXOG extend from 22 percent in some areas to 92 percent in other areas.

Populations at the southern rim of their native distributions, which may already be near their thermal limits, are likely to suffer more than populations near the center or northern portions of their ranges.

Problems could be particularly acute for species in the shallow rivers of the Southwest.

Fishes that prefer cool waters, such as smallmouth bass, striped bass and walleye, will be particularly sensitive to rising temperatures and ZLOO SXVK LQWR WKH QRUWKHUQ UHDFKHV RI WKHLU UDQJHV :KHUH ÀVK KDYH become adapted to cooler, more oxygen-rich waters, the combination of poor oxygenation and high temperatures will be especially SUREOHPDWLF DV VWUDWLÀHG ZDWHU ERGLHV VTXHH]H ÀVK EHWZHHQ ZDUP and cold layers of low-oxygen water.

Global warming could be disastrous for trout populations in lowelevation southern streams. Losses of 53 percent to 97 percent of wild trout in the Appalachian Mountains are predicted; remaining populations will likely be highly fragmented and restricted to isolated drainages, increasing their vulnerability and making natural recolonization improbable.

40 – SEASONS’ END: Global Warming’s Threat to Hunting and Fishing

The northern limits of most species are determined by the ability

dams or non-native predators. Where conditions exceed the adaptive

of the young to grow during warmer months and to survive low

FDSDELOLW\ RI WKH ÀVK ORFDO H[WLQFWLRQV RI VSHFLHV HYHQWXDOO\ RFFXU

temperatures in the colder months. Extended periods of cold lead to VWDUYDWLRQ DQG LQWHQVH FROG EHORZ D ÀVK¡V SK\VLRORJLFDO WKUHVKROG can be lethal.

As the thermal boundary of their ranges shifts upward and poleZDUG FRRO DQG FROG ZDWHU ÀVK PD\ SRSXODWH VRPH ZDWHUV WKDW KLVtorically have been inhospitably cold. Warmer stream temperatures FRXOG EHQHÀW VSHFLHV VXFK DV JUHHQEDFN FXWWKURDW WURXW ZKLFK KDV been limited by poor recruitment in cold headwaters at high elevations. The earlier spawning and faster growth rates predicted with

$PRQJ ÀVKHV DEOH WR PRYH WR PRUH IDYRUDEOH HQYLURQV JOREDO ZDUPing will cause shifts in distribution. Some species will avoid physiologically stressful conditions by abandoning traditional localities, either seasonally or permanently. :KLOH JOREDO ZDUPLQJ FRXOG UHVWULFW WKH PRYHPHQW RI ÀVK E\ UHGXFLQJ VWUHDP à RZ LW PD\ DOVR FUHDWH QHZ VWUHDP QHWZRUNV E\ PHOWLQJ glaciers and thawing permafrost. These networks could potentially increase connectivity among habitats and enhance colonization, promoting expansion for some species.

warmer stream temperatures will likely increase summer growth and the overwinter survival of these species.

stream and contracting headwater habitat, by increased landscape

Global Warming and Community Structure

GLVWXUEDQFHV IURP VWRUPV DQG ZLOGĂ€UHV DQG E\ KLJK WHPSHUDWXUHV

Global warming will alter freshwater conditions, disrupt interac-

evaporating water supplies. The range of some trout species is pre-

WLRQV DPRQJ ÀVKHV DQG VKLIW SDWWHUQV LQ WKH IRRG ZHE )LVKHV VXLWHG

dicted to decrease by as much as 80 percent. Such contraction will

to warm waters — such as bluegills, bass and perch — will move

OLNHO\ EH DFFRPSDQLHG E\ LQFUHDVHG IUDJPHQWDWLRQ RI ÀVK SRSXOD-

into waters vacated by cool- and cold-water species like walleye and

tions, further compounding the effects of shrinking habitat.

trout.

Species facing habitat fragmentation have literally no place to go.

Warming trends could also kill off predators. No longer controlled

&KDQJLQJ HQYLURQPHQWDO FRQGLWLRQV PD\ SURYLGH ÀVK QR RSWLRQV RU

by predation, species like smallmouth bass or brown trout could ex-

habitat may not allow egress to more favorable sites. Smaller stream

pand their ranges northward and compete for food and habitat with

Ă RZV FDQ OLPLW PRYHPHQW DV FDQ WKH SUHVHQFH RI VWHHS JUDGLHQWV

native salmonid populations.

However, gains could be erased by waters’ warming farther up-

FRESHWATER FISH – 41

$Q\ LQYDVLRQ E\ D VSHFLHV Âł Ă RUD RU IDXQD Âł QRW KLVWRULFDOO\ SUHV-

dampen wild populations’ instincts to adjust their migration and

ent in an ecosystem will cause some disruption, although a system’s

spawning patterns to changes in temperature and hydrology. The

exact response is impossible to predict. New species could be incor-

effects of climate change on the interactions between hatchery and

porated into the environment with relatively little disturbance and

ZLOG ÀVK SRSXODWLRQV ORRP DV DQ LQFUHDVLQJ FRQFHUQ LQ ÀVKHULHV

no long-term detriment. Or disruption could be widespread and re-

management.

sult in the suppression or even local extinction of native species.

Global warming is likely to support an increase in the numbers and an expansion of the ranges of exotic invasive species such as the New

Summary

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)UHVKZDWHU ÀVK VSHFLHV SDUWLFXODU WKRVH WKDW UHO\ RQ FROG ZDWHU

Limited by minimum temperatures or dependent on thermal refuge

habitat, will be dramatically affected by climate change. Reduced

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VXPPHU Ă RZV GXH WR ODFN RI VQRZPHOW ZLOO FRPELQH ZLWK JHQHUDOO\

areas of suitable habitat. Invasive species are particularly threaten-

higher temperatures to pose real risks to the survival of cold-water

ing in Florida, California and Texas, where favorable climates are

species like trout and salmon. It is predicted that up to 42 percent

OLNHO\ WR IRVWHU H[RWLF Ă RUD DQG IDXQD

of trout and salmon habitat will be lost within the next hundred

0DQDJHPHQW VWUDWHJLHV WR SURWHFW QDWLYH ÀVK SRSXODWLRQV FRXOG include erecting barriers to prevent invasion of an ecosystem. But because such practices could potentially isolate populations, managers must weigh the threat posed by invaders against the value RI SUHVHUYLQJ FRUULGRUV FRQQHFWLQJ QDWLYH ÀVK WR KDELWDWV XS DQG downstream.

years. In some regions, this will result in a 50 percent decline in population of those species. At lower elevations, entire populations of cold-water species may disappear, while even populations living at higher elevations will feel stress. Bass, bluegill and other warmwater species also will face stress from droughts, lower summer river Ă RZV DQG LQFUHDVLQJO\ VHYHUH Ă XFWXDWLRQV LQ ULYHU DQG ODNH OHYHOV This can affect the survival of eggs and jeopardize the recruitment

+DWFKHU\ ÀVK SRWHQWLDOO\ SRVH DQRWKHU WKUHDW WR ZLOG SRSXODWLRQV

RI DGXOW ÀVK 7KURXJKRXW WKH FRXQWU\ ZDUPHU ZDWHU WHPSHUDWXUHV

1RW GHSHQGHQW RQ VSDZQLQJ DQG UHDULQJ KDELWDW KDWFKHU\ ÀVK PD\

will lead to the expansion of noxious, exotic plants like hydrilla and

possess physiological, survival and competitive advantages over

Eurasian watermilfoil. Sea-level rise will push saline water farther

ZLOG SRSXODWLRQV 0L[LQJ JHQHV RI KDWFKHU\ DQG QDWLYH ÀVK PD\

upstream, in some cases reducing suitable freshwater habitat. At the

42 – SEASONS’ END: Global Warming’s Threat to Hunting and Fishing

same time, the ranges of certain warm-water species may increase with water temperatures rising in northern climes.

Scientists don’t know how climate change will affect every aspect of WKH ÀVKLQJ H[SHULHQFH EXW WKH\ GR NQRZ WKDW DQJOHUV VKRXOG FRXQW on change. In many lakes and rivers, water levels will suffer from higher evaporation rates, lower spring and early summer snowmelt and prolonged drought, making boat access more challenging.

Trout and salmon will disappear from many streams and rivers that today hold viable populations, severely diminishing opportunities WR FDWFK WKRVH VSHFLHV 0RUHRYHU ÀVKHU\ PDQDJHUV OLNHO\ ZLOO EH IRUFHG WR UHGXFH GDLO\ EDJ OLPLWV WR EHWWHU SURWHFW DGXOW ÀVK $V PRUH frequent droughts heighten competition for water resources among DOO XVHUV ERWK ÀVKHULHV PDQDJHUV DQG ÀVKHUPHQ PD\ QHHG WR JHW PRUH LQYROYHG LQ HIIRUWV WR SURWHFW LQVWUHDP à RZV 'HSHQGLQJ RQ where anglers live and practice their sport, they may need to change WKHLU WDUJHW ÀVK IURP FROG ZDWHU VSHFLHV WR PRUH UHVLOLHQW ZDUP water species or be prepared to travel longer distances to pursue their cold-water favorites.

FRESHWATER FISH – 43