american eels in the hudson river estuary: from glass to silver · • quick summary of previous hr...

American eels in the Hudson River estuary: from glass to silver

Karin E. Limburg, SUNY ESF Chris Bowser, Sarah Mount

Hudson River National Estuarine Research Res. NYSDEC Hudson River Estuary Program

Bob Schmidt (in absentia)

Outline of today’s talk:

• General biology of eel (emphasis on )

• Quick summary of previous HR eel studies

• Current HR eel studies

• Glass

• Yellow

• Silver

• Evolution from study object to a river icon that brings people together

Freshwater eels are catadromous – born at

sea, can migrate into estuaries, rivers, streams, lakes…even stay at sea

Eels have a complex set of life stages:

Larvae – specialized to drift, called leptocephali (pl.)

Transform in estuaries into transparent glass eels

Develop yellow-brown pigmentation – called elvers

bootlace eels yellow phase silver (maturing,

migrating back to sea)

It wasn’t until an enterprising Dane, Johannes Schmidt, began a long-term examination of fisheries collections that we understood the life cycle of eels.

Beginning in 1904, Schmidt received grants from the Danish queen to send out ships into the middle of the Atlantic, to collect fish larvae.

Finally, in 1922, the smallest larvae were collected south of Bermuda in the Sargasso Sea…the mysterious part of the Atlantic with depths over 5,000 meters.

The further the ships went into the heart of the Atlantic, the smaller the leptocephali.

www.jang-eo.co.kr/a1.html

Source: Maryland Sea Grant

Source: Uwe Kils, Rutgers University

American eel leptocephali

Tesch, 1977

Capable of climbing vertical surfaces – capillary action - “glass walls” of old

Now, heavily exploited fishery

Source: Glooskap and the Frog

Glass eels swim up estuaries in droves

Yellow eels (growth phase)

• can live in a wide variety of habitats

• varied diets (leads to morphological variation their skulls)

• growth rates highly variable

• accumulate fat for the long migration back to Sargasso

As eels become ready to migrate to the Sargasso, they become silvery and their eyes enlarge – cease feeding

Pankhurst’s index = a measure of eye size (a maturation index)

Source: van Ginneken & van Theillart, U. Leiden

American eel life history

DFO Canada Scientific American

Age vs length

25

35

45

55

65

0 5 10 15 20 25 30

Age (years)

Le

ng

th (

cm

)

Gwb Hav New King Ath Alb

ALBANY

ATHENS

KINGSTON

km

245

200

145

105

55

20

salt

front

HAVERSTRAW

NEWBURGH

G.W. BRIDGE

Hugely variable growth rates!

Early HR eel studies

Hudson River yellow eel study 1997-99

– W. Morrison & D. Secor, U. MD

GWB eel#33, length = 49 cm

Example of variable growth seen in eel otoliths

Kingston eel#36, length = 45 cm

Source: Wendy Morrison, U. MD

Hudson River km 20

Hudson River km 145

Estuarine growth (fast)

Upriver/tributary growth

Hudson River tributaries study

2003-04 … the first,

featuring Leonard Machut (ESF M.Sc.)

Natural and artificial barriers act as filters that reduce the numbers of eels upstream

The Glass Eel Story, or The Young and the Wiggly

The Hudson River Glass Eel Project Albany

NYC

• Spans 150 miles of tidal estuary from Staten Island (salt) to near Albany (fresh)

• Variety of methods, sites, and audiences

• Springtime focus on YOY/glass eels/elvers

Using fyke nets to monitor glass eels

• Each spring, nets are placed in the mouths of streams • Teams of trained volunteers catch, count, and release eels • Project follows ASMFC methods

450,000+ juvenile eels caught &

released above barriers since 2008

550 volunteers at 12 sites in 2016

2388 8561 9303 7382

61555

90929

41816 48158

140942

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

2008 2009 2010 2011 2012 2013 2014 2015 2016

Total glass eel catch for all sites

Average Eels Caught Per Day Per Year

15

41 29

18

125

203

93

110

239

0

50

100

150

200

250

300

2008 2009 2010 2011 2012 2013 2014 2015 2016

38

58

64

75

67

46

66

58

75

0

10

20

30

40

50

60

70

80

2008 2009 2010 2011 2012 2013 2014 2015 2016

Average Glass Eels/Day at Furnace Brook

Albany

NYC

22

51 38

10

106 125

311

184

428

0

50

100

150

200

250

300

350

400

450

2008 2009 2010 2011 2012 2013 2014 2015 2016

Average Glass Eels/Day at Fall Kill

Albany

NYC

22

51 38

10

106 125

311

184

428

0

50

100

150

200

250

300

350

400

450

2008 2009 2010 2011 2012 2013 2014 2015 2016

Average Glass Eels/Day at Fall Kill

Furnace Brook range: 38-75 glass eels/day

Albany

NYC

0

400

800

1200

1600

2000

3/25 4/4 4/14 4/24 5/4 5/14 5/24

Albany

NYC 4/14

Number of glass eels per collection period (approx. 24 hours)

0

400

800

1200

1600

2000

3/25 4/4 4/14 4/24 5/4 5/14 5/24

Minisceongo Creek

Albany

NYC 4/14

4/21

Number of glass eels per collection period (approx. 24 hours)

0

400

800

1200

1600

2000

3/25 4/4 4/14 4/24 5/4 5/14 5/24

Richmond Creek

Minisceongo Creek

Crum Elbow Creek

Albany

NYC 4/14

4/21

5/4

Number of glass eels per collection period (approx. 24 hours)

0

400

800

1200

1600

2000

3/25 4/4 4/14 4/24 5/4 5/14 5/24

Richmond Creek

Minisceongo Creek

Crum Elbow Creek

Saw Kill

Albany

NYC 4/14

4/21

5/6

5/10

In 2014 we tracked the speed of glass eels upriver

10.7

4.8

2.4

Date, 2014

# e

els

per

day

29

“Eel Mop” at Saw Mill River

“Eel-evators” to get eels past dams (May-Oct)

# Eels caught at Furnace Brook Ladder in 2011 & 2012 (sampling season May through October)

< 8 8-15 15-30 >30

2011

2012

Eel lengths in centimeters

“Assessing Provenance and Maturity Status of Hudson River Eels”

Yellow phase HR eels: Provenance studies using otolith chemistry

Artificial tag

An eel otolith (Photo: L. Machut)

Otoliths

(“ear-stones”)

An eel otolith (11-12 yrs old)

Here, we show results of analyzing the outermost 100 microns of material for 7 element/Calcium ratios + 26/24Mg isotopes…next slide…

Plot of Can2*Can1$Tributary. Symbol used is '*'. „ƒˆƒƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒƒˆƒƒ† Can2 ‚ ‚ ‚ ‚ 4 ˆ ˆ ‚ ‚ ‚ * Indian Kill ‚ ‚ ‚ ‚ ‚ ‚ Indian Kill Black Creek * ‚ 2 ˆ * * Crum Elbow Kill Black Creek * ˆ ‚ Crum ElbownKill Kil** *rum Elbow Kill ‚ ‚ Indian Kil* * *Indian Kill ‚ ‚ Indian Fal* *illIn*ian*KVlockie Kill ‚ ‚ Crum Elbow*Killn*Cru*KEl*ow Kill ‚ ‚ Crum Elbow Kill***aVlocill*K*lC*um Elbow Kill Black Creek * ‚ 0 ˆ Fall Crum *lbowVlo*l*eCrumlElbow Kill * Vlockie Kill ˆ ‚ Fall Kill** Indi*n **Crum Elbow K*lVlockie Kill ‚ ‚ Fall Kill*Indian*Kill * Black *reek ‚ ‚ Fall*KFall*Kill Vlockie Kill ‚ ‚ * Fall Kill Fall*Kill * Minisceongo Creek ‚ ‚ Minisceongo*Creek ‚ -2 ˆ Minisceon*oMinieceongo Creek ˆ ‚ Crum Elbow Kill * * Minisceongo Creek ‚ ‚ * Fall Kill ‚ ‚ * Minisceongo Creek ‚ ‚ * Minisceongo Creek ‚ ‚ ‚ -4 ˆ ˆ ‚ ‚ ŠƒˆƒƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒƒˆƒƒƒƒƒƒƒƒƒƒƒƒˆƒƒŒ -4 -2 0 2 4 6 Can1 NOTE: 1 obs hidden. 63 label characters hidden.

BC

CE

FK

IK

MC

VK

Canonical Discriminant Analysis of 53 eels

(Apologies for SAS output!)

Number of Observations and Percent Classified into Tributary

From Tributary

Black

Creek

Crum

Elbow

Kill

Fall

Kill

Indian

Kill

Mini-

sceongo

Creek

Vlockie

Kill Total

Black Creek 4

100%

0

0.00

0

0.00

0

0.00

0

0.00

0

0.00

4

100.00

Crum Elbow Kill 0

0.00 13

100%

0

0.00

0

0.00

0

0.00

0

0.00

13

100.00

Fall Kill 0

0.00

0

0.00 11

100%

0

0.00

0

0.00

0

0.00

11

100.00

Indian Kill 0

0.00

0

0.00

0

0.00 12

100%

0

0.00

0

0.00

12

100.00

Minisceongo Creek 0

0.00

0

0.00

0

0.00

0

0.00 7

100%

0

0.00

7

100.00

Vlockie Kill 0

0.00

0

0.00

0

0.00

0

0.00

0

0.00 6

100%

6

100.00

Total 4

7.55

13

24.53

11

20.75

12

22.64

7

13.21

6

11.32 53

100%

Priors 0.16667

0.16667

0.16667

0.16667

0.16667

0.16667

All 53 eels were correctly classified to the tributary where they were captured

Photos: Dave Yozzo

Silver Eel Studies

1. American eels (Anguilla rostrata) hatch here

Béguer-Pon et al. 2015

Tagging adult eels

Béguer-Pon et al. 2015

Silver eel research Goals:

• Better understand transition from yellow (resident) to silver (migratory)

• Develop a non-lethal index of maturity for American eels that can be used by researchers and managers

Why? To easily assess eel productivity in the field based on quantitative measures

Methods

NYC

Electrofishing

Fyke netting

Albany

NYC

External measurements (≥25cm) • Total length • Wet weight • Horizontal and vertical

eye diameter • Head length • Head width • Pectoral fin length • Body depth

Clusters by size

± S.E.

0

100

200

300

400

500

600

700

SilverF SilverM Yellow YellowF

Tota

l len

gth

, mm

Maturity class

Clusters by eye and fin index

0

2

4

6

8

10

SilverF SilverM Yellow YellowF

Pan

khu

srt

eye

ind

ex

• Pankhurst eye index separates eels into mature (silver) or immature (yellow) • Threshold = 6.5

• Mature eels have higher eye index, above threshold

Clusters by eye and fin index

0

2

4

6

8

10

SilverF SilverM Yellow YellowF

Pan

khu

srt

eye

ind

ex

0

1

2

3

4

5

6

SilverF SilverM Yellow YellowF

Pect

ora

l fin

ind

ex

• Pankhurst eye index separates eels into mature (silver) or immature (yellow) • Threshold = 6.5

• Mature eels have higher eye index, above threshold

• Fin index also significantly different between silver and yellow eels

Discriminant analysis • Correctly classify individuals 83% of the time overall

Predicted maturity stage

SilverF SilverM1 SilverM2 Yellow1 Yellow2 YellowF1 YellowF2 Total

SilverF 13

87%

0

0%

0

0%

0

0%

0

0%

0

0%

2

13.33%

15

SilverM1 0

0%

17

94%

1

5.56%

0

0%

0

0%

0

0%

0

0%

18

SilverM2 0

0%

0

0%

17

85%

0

0%

3

15%

0

0%

0

0%

20

Yellow1 0

0%

1

0.5%

2

1%

160

80%

34

16.92%

4

1.99%

0

0%

201

Yellow2 0

0%

1

2.04%

0

0%

2

4.08%

46

94%

0

0%

0

0%

49

YellowF1 1

5.88%

0

0%

0

0%

2

11.76%

0

0%

12

71%

2

11.76%

17

YellowF2 0

0%

0

0%

0

0%

1

12.5%

0

0%

0

0%

7

88%

8

Act

ual

matu

rity

sta

ge

Mark-Recapture on the Indian Kill

So far we’ve: • Tagged 347 eels • Recaptured 110

eels at least once

Methods allow us to investigate: • Growth

(~1 cm/year) • Movement

(62% don’t move) • Maturity

Albany

NYC

Data Story of Eel Maturity

July, 2014 4x4 mm eye diameter 14 mm fin length

Marsh

Albany

NYC

Data Story of Eel Maturity

July, 2014 4x4 mm eye diameter 14 mm fin length

October, 2014 6x6 mm eye diameter 17 mm fin length

Marsh

Albany

NYC

Data Story of Eel Maturity

July, 2014 4x4 mm eye diameter 14 mm fin length

October, 2014 6x6 mm eye diameter 17 mm fin length

Marsh

Heading to the Sargasso!

Albany

NYC

Timing of maturity clusters

0

10

20

30

40

50

60

70

80

90

100

Jul 2013 Aug 2013 Sep 2013 Fyke 2013 Jul 2014 Aug 2014 Sep 2014 Fyke 2014

% e

els

cau

ght

SilverF SilverM Yellow

Summary of silver eel research • Research tools important in future studies

• Non-lethal maturity index has fairly high classification rates

• Could be used in future studies to: • Assess eel productivity – how many mature eels out of

total numbers

• Paired with data on other life stages, could calculate survivorship from one life stage to the next

• Compare maturity breakdown in different habitat types

Respect Your Elvers!

Evolution from study object to a river icon

that brings people together…

Respect Your Elvers! Evolution from study object to a river icon

that brings people together…and reconnects waters

Respect Your Elvers! Evolution from study object to a river icon

that brings people together…and reconnects waters

Working with students and volunteers!

“There is life against all odds in places where you would think there is nothing. Interesting opportunities exist in the scientific

community for amateur naturalists to make a contribution.” --volunteer Eva Schadeck

“At first, I only did it for extra credit, but then I realized it was really cool!”

--Poughkeepsie High School student

Thank you for listening!

Thank you, HRF, NYSDEC, and especially Cara Ewell Hodkin and Kayla Smith for helping with oto-analyses

Bob Schmidt

External cluster analysis

• 983 individuals total

• Separated into 7 significantly different clusters

Using fyke nets to monitor glass eels

• Each spring, nets are placed in the mouths of streams • Teams of trained volunteers catch, count, and release eels • Project follows ASMFC methods •http://www.youtube.com/watch?v=j-tik6Y9ztA •http://www.youtube.com/watch?v=gfCvxIgSw_s